Motor assembly

ABSTRACT

A motor assembly includes a motor, a housing including a housing space to house the motor, oil in a vertically lower region of the housing space, and an oil passage to lead the oil from the vertically lower region of the housing space through the motor to the vertically lower region of the housing space. The oil passage includes a first oil passage extending through an inside of the motor, and a second oil passage extending through an outside of the motor. One of the first oil passage and the second oil passage includes a cooler to cool the oil therein.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to a motor assembly.

2. Description of the Related Art

There is known a structure in which a flow passage arranged to passthrough an interior of a shaft to cool a motor, and a flow passagearranged to feed an oil from an upper side of a stator to cool themotor, are provided.

In the case of the known structure, a flow passage at which the two flowpassages join is provided in addition to the two flow passages, and acooling device to cool a coolant is arranged in the combined flowpassage. This may involve complicated structures of the flow passages,and may lead to a high cost.

SUMMARY OF THE INVENTION

A motor assembly according to an example embodiment of the presentdisclosure includes a motor, a housing including a housing space tohouse the motor, oil in a vertically lower region of the housing space,and an oil passage to lead the oil from the vertically lower region ofthe housing space through the motor to the vertically lower region ofthe housing space. The oil passage includes a first oil passageextending through an inside of the motor, and a second oil passageextending through an outside of the motor. One of the first oil passageand the second oil passage includes a cooler to cool the oil therein.

The above and other elements, features, steps, characteristics andadvantages of the present disclosure will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a motor assembly according to anexample embodiment of the present disclosure.

FIG. 2 is a perspective view of the motor assembly according to anexample embodiment of the present disclosure.

FIG. 3 is a side view of the motor assembly according to an exampleembodiment of the present disclosure.

FIG. 4 is a sectional view of the motor assembly taken along line IV-IVin FIG. 3.

FIG. 5 is a sectional view of a rotor according to an example embodimentof the present disclosure.

FIG. 6 is a plan of an end plate.

FIG. 7 is a sectional view of the end plate taken along line VII-VII inFIG. 6.

FIG. 8 is a sectional view of an end plate according to a firstmodification of an example embodiment of the present disclosure.

FIG. 9 is a plan of an end plate according to a second modification ofan example embodiment of the present disclosure.

FIG. 10 is a sectional view of the motor assembly according to anexample embodiment of the present disclosure, illustrating a second oilpassage.

FIG. 11 is a perspective view of the motor assembly according to anexample embodiment of the present disclosure in which portions of ahousing are not shown.

FIG. 12 is a plan of a second reservoir according to an exampleembodiment of the present disclosure.

FIG. 13 is a perspective view of a second reservoir according to amodification of an example embodiment of the present disclosure.

FIG. 14 is a sectional view of the motor assembly according to anexample embodiment of the present disclosure, illustrating an outline ofan auxiliary reservoir.

FIG. 15 is a front view of a partition opening according to an exampleembodiment of the present disclosure.

FIG. 16 is a graph showing the relationship between the level of aliquid level of oil in a lower region of a motor chamber and the area ofa first region in the motor assembly according to an example embodimentof the present disclosure.

FIG. 17 is a front view of a partition opening according to amodification of an example embodiment of the present disclosure.

FIG. 18 is a graph showing the relationship between the level of aliquid level of oil in a lower region of a motor chamber and the area ofa first region in a motor assembly including the partition openingaccording to a modification of an example embodiment of the presentdisclosure.

FIG. 19 is a side view illustrating the arrangement of gears in a gearchamber of the motor assembly according to an example embodiment of thepresent disclosure.

FIG. 20 is a plan of a parking mechanism that can be adopted in themotor assembly according to an example embodiment of the presentdisclosure.

FIG. 21 is a partial sectional view illustrating a separating mechanismof a motor assembly according to Modification 1 of an example embodimentof the present disclosure.

FIG. 22 is a schematic diagram illustrating a situation in which a motorand a reduction gear are connected to each other through the separatingmechanism.

FIG. 23 is a schematic diagram illustrating a situation in which themotor and the reduction gear have been separated from each other by theseparating mechanism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, motors according to embodiments of the present disclosurewill be described with reference to the accompanying drawings. Note thatthe scope of the present disclosure is not limited to the embodimentsdescribed below, but includes any modification thereof within the scopeof the technical idea of the present disclosure. Also note that scales,numbers, and so on of members or portions illustrated in the followingdrawings may differ from those of actual members or portions, for thesake of easier understanding of the members or portions.

The following description will be made with the direction of gravitybeing defined on the basis of positional relationships in the case wherea motor assembly 1 is installed in a vehicle on a horizontal roadsurface. In addition, in the drawings, an xyz coordinate system is shownappropriately as a three-dimensional orthogonal coordinate system. Inthe xyz coordinate system, a z-axis direction corresponds to a verticaldirection (i.e., an up-down direction), and a +z direction points upward(i.e., in a direction opposite to the direction of gravity), while a −zdirection points downward (i.e., in the direction of gravity). Inaddition, an x-axis direction corresponds to a front-rear direction ofthe vehicle in which the motor assembly 1 is installed, and is adirection perpendicular to the z-axis direction, and a +x directionpoints forward of the vehicle, while a −x direction points rearward ofthe vehicle. Note, however, that the +x direction and the −x directionmay point rearward and forward, respectively, of the vehicle. A y-axisdirection is a direction perpendicular to both the x-axis direction andthe z-axis direction, and is a width direction (i.e., a left-rightdirection) of the vehicle.

In the following description, unless otherwise specified, a direction(i.e., the y-axis direction) parallel to a motor axis J2 of a motor 2will be simply referred to by the term “axial direction”, “axial”, or“axially”, radial directions centered on the motor axis J2 will besimply referred to by the term “radial direction”, “radial”, or“radially”, and a circumferential direction centered on the motor axisJ2, i.e., a circumferential direction about the motor axis J2, will besimply referred to by the term “circumferential direction”,“circumferential”, or “circumferentially”. Further, in the followingdescription, the term “plan view” refers to a view as seen in the axialdirection. Note, however, that the term “parallel” as used aboveincludes both “parallel” and “substantially parallel”. Also note thatthe term “perpendicular” as used above includes both “perpendicular” and“substantially perpendicular”.

Hereinafter, a motor assembly (i.e., an electric drive machine) 1according to an exemplary embodiment of the present disclosure will bedescribed with reference to the drawings.

FIG. 1 is a schematic diagram of the motor assembly 1 according to anembodiment. FIG. 2 is a perspective view of the motor assembly 1. FIG. 3is a side view of the motor assembly 1. FIG. 4 is a sectional view ofthe motor assembly 1 taken along line IV-IV in FIG. 3. Note that, inFIG. 4, part of an internal structure of a differential 5 is not shown.

The motor assembly 1 is installed in a vehicle having a motor as a powersource, such as, for example, a hybrid electric vehicle (HEV), a plug-inhybrid vehicle (PHV), or an electric vehicle (EV), and is used as thepower source thereof.

Referring to FIG. 1, the motor assembly 1 includes a motor (i.e., a mainmotor) 2, a reduction gear 4, the differential 5, a housing 6, an oil O,and an oil passage 90 arranged to feed the oil O to the motor 2. Inaddition, the motor assembly 1 may include a parking mechanism 7 asindicated by an imaginary line in FIG. 2.

Referring to FIG. 1, the motor 2 includes a rotor 20 arranged to rotateabout the motor axis J2, which extends in a horizontal direction, and astator 30 arranged radially outside of the rotor 20. The reduction gear4 is connected to the rotor 20 of the motor 2. The differential 5 isconnected to the motor 2 through the reduction gear 4. A housing space80, in which the motor 2, the reduction gear 4, and the differential 5are housed, is defined inside of the housing 6. The oil O is used tolubricate the reduction gear 4 and the differential 5, and is also usedto cool the motor 2. The oil O is gathered in a vertically lower regionof the housing space 80. An oil equivalent to a lubricating oil (ATF:Automatic Transmission Fluid) for an automatic transmission having a lowviscosity is preferably used as the oil O so that the oil O can performfunctions of a lubricating oil and a cooling oil. The oil passage 90 isa channel of the oil O along which the oil O is fed from the lowerregion of the housing space 80 to the motor 2. The oil passage 90includes a first oil passage 91 and a second oil passage 92.

Note that, in the present specification, the term “oil passage” refersto a channel along with the oil O circulates in the housing space 80.Therefore, the “oil passage” is a concept that includes not only a “flowpassage”, in which a steady flow of an oil steadily traveling in onedirection is formed, but also a channel (e.g., a reservoir) in which theoil is allowed to temporarily stay, and a channel along which the oildrips.

The motor 2, the reduction gear 4, and the differential 5 are housed inthe housing space 80 defined inside of the housing 6. The housing 6 isarranged to hold the motor 2, the reduction gear 4, and the differential5 in the housing space 80. The housing 6 includes a partition 61 c. Thehousing space 80 of the housing 6 is divided by the partition 61 c intoa motor chamber 81 and a gear chamber 82. The motor 2 is housed in themotor chamber 81. The reduction gear 4 and the differential 5 are housedin the gear chamber 82.

An oil pool P, i.e., a pool of the oil O, is arranged in the lowerregion of the housing space 80. In the present embodiment, a bottomportion 81 a of the motor chamber 81 is arranged higher than a bottomportion 82 a of the gear chamber 82. In addition, a lower region of thepartition 61 c, which is arranged to divide the motor chamber 81 and thegear chamber 82, includes a partition opening 68. The partition opening68 is arranged to bring the motor chamber 81 and the gear chamber 82into communication with each other. The partition opening 68 allows aportion of the oil O which has been gathered in a lower region of themotor chamber 81 to be transferred to the gear chamber 82 therethrough.Therefore, in the present embodiment, the oil pool P is arranged in alower region of the gear chamber 82.

A portion of the differential 5 soaks in the oil pool P. The oil Ogathered in the oil pool P is scraped up by an operation of thedifferential 5, and a portion thereof is fed to the first oil passage91, and another portion thereof is spread within the gear chamber 82.The portion of the oil O which has been spread within the gear chamber82 is fed to various gears of the differential 5 and the reduction gear4 within the gear chamber 82, so that the oil O spreads throughout toothfaces of the gears. Portions of the oil O which have been used by thereduction gear 4 and the differential 5 drip, and are collected into theoil pool P in the lower region of the gear chamber 82. The capacity ofthe oil pool P in the housing space 80 is set such that a portion of abearing of the differential 5 will soak in the oil O when the motorassembly 1 is in a stopped state.

The housing 6 is produced by, for example, an aluminum die-castingprocess. The housing 6 defines an outer frame of the motor assembly 1.The housing 6 includes a motor housing portion 61, a gear housingportion 62, and a closing portion 63. The gear housing portion 62 isarranged to the left of the motor housing portion 61. The closingportion 63 is arranged to the right of the motor housing portion 61.

The motor housing portion 61 includes a tubular peripheral wall portion61 a arranged to surround the motor 2 from radially outside, and a sideplate portion 61 b arranged on one axial side of the peripheral wallportion 61 a. A space inside of the peripheral wall portion 61 a definesthe motor chamber 81. The side plate portion 61 b includes the partition61 c and a projecting plate portion 61 d. The partition 61 c is arrangedto cover an opening of the peripheral wall portion 61 a on the one axialside. In addition to the aforementioned partition opening 68, an inserthole 61 f, through which a shaft 21 of the motor 2 is inserted, isdefined in the partition 61 c. The side plate portion 61 b includes thepartition 61 c and the projecting plate portion 61 d, which is arrangedto project radially outward relative to the peripheral wall portion 61a. A first axle insertion hole 61 e, through which a drive shaft (notshown) arranged to support a wheel is arranged to pass, is defined inthe projecting plate portion 61 d.

The closing portion 63 is fixed to the motor housing portion 61. Theclosing portion 63 is arranged to close an opening of the peripheralwall portion 61 a on another axial side. That is, the closing portion 63is arranged to close an opening of the motor housing portion 61, whichis tubular. The closing portion 63 includes a main closing portion body63 a and a cover member 63 b. The main closing portion body 63 aincludes a tubular projecting portion 63 d arranged to project into thehousing space 80 arranged inside of the motor housing portion 61. Theprojecting portion 63 d is arranged to extend along an inner peripheralsurface of the peripheral wall portion 61 a. In addition, the mainclosing portion body 63 a includes a window portion 63 c arranged topass therethrough in the axial direction. The cover member 63 b isarranged to close the window portion 63 c from outside of the housingspace 80.

The gear housing portion 62 is fixed to the side plate portion 61 b ofthe motor housing portion 61. The gear housing portion 62 is arranged tohave a recessed shape, and is arranged to open toward the side plateportion 61 b. An opening of the gear housing portion 62 is covered bythe side plate portion 61 b. A space between the gear housing portion 62and the side plate portion 61 b defines the gear chamber 82, which isarranged to house the reduction gear 4 and the differential 5. A secondaxle insertion hole 62 e is defined in the gear housing portion 62. Thesecond axle insertion hole 62 e is arranged to coincide with the firstaxle insertion hole 61 e when viewed in the axial direction.

Referring to FIG. 3, the gear housing portion 62 has a first reservoir(i.e., a reservoir) 93 and a shaft feed flow passage 94. The firstreservoir 93 is arranged to extend along the axial direction at asurface of the gear housing portion 62 which faces onto the gear chamber82 in the axial direction. The first reservoir 93 is arranged to receivea portion of the oil O which has been scraped up by the differential 5.The shaft feed flow passage 94 is arranged to extend from a bottomportion of the first reservoir 93 toward the shaft 21 of the motor 2.The shaft feed flow passage 94 is a flow passage arranged to feed theoil O received by the first reservoir 93 into a hollow portion 22 of theshaft 21.

Referring to FIG. 4, the reduction gear 4 has a function of increasing atorque outputted from the motor 2 while reducing the rotation speed ofthe motor 2 in accordance with a reduction ratio. The reduction gear 4is arranged to transfer the torque outputted from the motor 2 to thedifferential 5.

The reduction gear 4 includes a first gear (i.e., an intermediate drivegear) 41, a second gear (i.e., an intermediate gear) 42, a third gear(i.e., a final drive gear) 43, and an intermediate shaft 45. The torqueoutputted from the motor 2 is transferred to a ring gear (i.e., a gear)51 of the differential 5 through the shaft 21 of the motor 2, the firstgear 41, the second gear 42, the intermediate shaft 45, and the thirdgear 43. The number of gears, the gear ratios of the gears, and so oncan be modified in various manners in accordance with a desiredreduction ratio. The reduction gear 4 is a speed reducer of aparallel-axis gearing type, in which center axes of gears are arrangedin parallel with each other.

The first gear 41 is arranged on an outer circumferential surface of theshaft 21 of the motor 2. The first gear 41 is arranged to rotate aboutthe motor axis J2 together with the shaft 21.

The intermediate shaft 45 is arranged to extend along an intermediateaxis J4 parallel to the motor axis J2. The intermediate shaft 45 isarranged to have a cylindrical shape with the intermediate axis J4 as acenter. The intermediate shaft 45 is arranged to rotate about theintermediate axis J4. The intermediate shaft 45 is rotatably supportedby a pair of intermediate shaft holding bearings 87. One of the pair ofintermediate shaft holding bearings 87 is held by a surface of thepartition 61 c which faces onto the gear chamber 82. Another one of thepair of intermediate shaft holding bearings 87 is held by the gearhousing portion 62.

Each of the second gear 42 and the third gear 43 is arranged on an outercircumferential surface of the intermediate shaft 45. The second gear 42and the third gear 43 are connected to each other through theintermediate shaft 45. Each of the second gear 42 and the third gear 43is arranged to rotate about the intermediate axis J4. The second gear 42is arranged to mesh with the first gear 41. The third gear 43 isarranged to mesh with the ring gear 51 of the differential 5. The thirdgear 43 is arranged on a side of the second gear 42 closer to thepartition 61 c. In the present embodiment, the intermediate shaft 45 andthe third gear 43 are defined by a single monolithic member.

The differential 5 is a device arranged to transfer the torque outputtedfrom the motor 2 to wheels of the vehicle. The differential 5 has afunction of transferring the same torque to axles 55 of left and rightwheels while absorbing a difference in speed between the left and rightwheels when the vehicle is turning. The differential 5 includes the ringgear 51, a gear housing 57, a pair of pinion gears (not shown), a pinionshaft (not shown), and a pair of side gears (not shown).

The ring gear 51 is arranged to rotate about a differential axis J5parallel to the motor axis J2. The torque outputted from the motor 2 istransferred to the ring gear 51 through the reduction gear 4. That is,the ring gear 51 is connected to the motor 2 with other gearsintervening therebetween. The ring gear 51 is fixed to an outercircumference of the gear housing 57.

The gear housing 57 is arranged to house the pair of pinion gears andthe pair of side gears. The gear housing 57 is arranged to rotate aboutthe differential axis J5 together with the ring gear 51 once the torqueis transferred to the ring gear 51.

The pair of pinion gears are bevel gears arranged to face each other.The pair of pinion gears are supported by the pinion shaft.

The pair of side gears are bevel gears arranged to mesh with the pair ofpinion gears at right angles. Each of the pair of side gears includes afitting portion. An axle is fitted to each of the fitting portions. Thepair of axles, each of which is fitted to a different one of the fittingportions, rotate about the differential axis J5 with the same torque.

Referring to FIG. 4, the motor 2 is an inner-rotor motor including thestator 30 and the rotor 20, which is rotatably arranged inside of thestator 30. The rotor 20 is caused to rotate by power being supplied froma battery (not shown) to the stator 30. The torque of the motor 2 istransferred to the differential 5 through the reduction gear 4.

The stator 30 includes a stator core 32, coils 31, and an insulator (notshown) arranged between the stator core 32 and the coils 31. The stator30 is held by the housing 6.

The stator core 32 includes a plurality of magnetic pole teeth (notshown) arranged to project radially inward from an inner circumferentialsurface of an annular yoke. The stator core 32 according to the presentembodiment is arranged to have 48 slots, each of which is definedbetween adjacent ones of the magnetic pole teeth. Wound coil wires arearranged between the magnetic pole teeth to define the coils 31.

Each coil 31 includes coil ends 31 a arranged to project from axial endsurfaces of the stator core 32. That is, the stator 30 includes the coilends 31 a. Each coil end 31 a is arranged to project in the axialdirection relative to an end portion of a rotor core 24 of the rotor 20.The coil ends 31 a are arranged to project to both axial sides relativeto the rotor core 24.

The rotor 20 includes the shaft (i.e., a motor shaft) 21, the rotor core24, rotor magnets (i.e., permanent magnets) 25, a pair of plate-shapedend plates 26, a nut 29, and a washer (i.e., a cover portion) 28.

The shaft 21 is arranged to extend with the motor axis J2, which extendsin a horizontal direction that is a width direction (i.e., a directionperpendicular to the direction of travel of the vehicle) of the vehicle,as a center. The shaft 21 includes a first shaft portion 21A and asecond shaft portion 21B coupled to each other so as to be coaxial.

The shaft 21 is a hollow shaft in which the hollow portion 22, which hasan inner circumferential surface arranged to extend along the motor axisJ2, is defined. The hollow portion 22 includes a first hollow portion22A arranged inside the first shaft portion 21A, and a second hollowportion 22B arranged inside the second shaft portion 21B. The firsthollow portion 22A and the second hollow portion 22B are arranged alongthe axial direction, and are in communication with each other.

The first shaft portion 21A is arranged in the motor chamber 81 of thehousing space 80. The first shaft portion 21A is arranged radiallyinside of the stator 30, and is arranged to pass through the rotor core24 along the motor axis J2. The first shaft portion 21A includes a firstend portion 21 e arranged on an output side (i.e., a side closer to thereduction gear 4), and a second end portion 21 f arranged on an oppositeside.

The first shaft portion 21A is rotatably supported by a pair of firstbearings 89. The pair of first bearings 89 are arranged to support thefirst end portion 21 e and the second end portion 21 f of the firstshaft portion 21A. One of the pair of first bearings 89 is held by theclosing portion 63. Another one of the pair of first bearings 89 is heldby a surface of the partition 61 c which faces onto the motor chamber81.

FIG. 5 is a sectional view of the rotor 20. Note that, in FIG. 5, thesecond shaft portion 21B is represented by imaginary lines.

A pair of communicating holes 23 are defined in the first shaft portion21A. Each communicating hole 23 is arranged to extend in a radialdirection to bring a space outside of the shaft 21 and the hollowportion 22 into communication with each other. That is, the pair ofcommunicating holes 23 are defined in the shaft 21. The pair ofcommunicating holes 23 are arranged along the axial direction. Note thatit is assumed in the present specification that each communicating hole23 is a hole extending from the outer circumferential surface of theshaft 21 through the hollow portion to the outer circumferentialsurface.

A collar portion (i.e., a cover portion) 21 c and a screw portion 21 dare arranged along the axial direction on an outer circumferentialsurface of the first shaft portion 21A. That is, the collar portion 21 cand the screw portion 21 d are arranged on the outer circumferentialsurface of the shaft 21. The rotor core 24 is arranged between thecollar portion 21 c and the screw portion 21 d in the axial direction.The nut 29 is screwed onto the screw portion 21 d.

Referring to FIG. 4, the second shaft portion 21B is arranged to becoaxial with the first shaft portion 21A. The second shaft portion 21 bincludes a third end portion 21 g arranged on a side closer to the firstshaft portion 21A, and a fourth end portion 21 h arranged on an oppositeside. The second shaft portion 21B is connected to the first end portion21 e of the first shaft portion 21A at the third end portion 21 g.

The second shaft portion 21B is arranged in the gear chamber 82 of thehousing space 80. The third end portion 21 g of the second shaft portion21B is arranged to project toward the motor chamber 81 through theinsert hole 61 f defined in the partition 61 c, and is connected to thefirst shaft portion 21A. The first gear 41 is arranged on an outercircumferential surface of the second shaft portion 21B. The first gear41 is a portion of the reduction gear 4. The first gear 41 is arrangedto mesh with the second gear 42 to transfer an output from the shaft 21to the second gear 42.

The second shaft portion 21B is rotatably supported by a pair of secondbearings 88. One of the pair of second bearings 88 is held by a surfaceof the partition 61 c which faces onto the gear chamber 82. Another oneof the pair of second bearings 88 is held by the gear housing portion62.

The hollow portion 22 is arranged to open in the axial direction at thesecond end portion 21 f of the first shaft portion 21A and the fourthend portion 21 h of the second shaft portion 21B. The oil O is fed intothe hollow portion 22 through an opening of the fourth end portion 21 h.The oil O fed into the hollow portion 22 flows from the fourth endportion 21 h toward the second end portion 21 f. The oil O fed into thehollow portion 22 flows out of the shaft 21 through the communicatingholes 23.

Note that, in the following description, a side of the hollow portion 22closer to the fourth end portion 21 h and a side of the hollow portion22 closer to the second end portion 21 f may sometimes be referred to asan upstream side and a downstream side, respectively, with respect tothe direction of flow.

Referring to FIG. 5, the first hollow portion 22A includes a firstregion 22 p, a second region (i.e., a small-diameter hollow portion) 22q, and a third region (i.e., a large-diameter hollow portion) 22 r, thediameters of inner circumferential surfaces of which are different fromone another. The diameters of the inner circumferential surfaces of thefirst region 22 p, the second region 22 q, and the third region 22 r areincreasingly greater in this order. That is, the second region 22 q hasan inside diameter greater than that of the first region 22 p, and thethird region 22 r has an inside diameter greater than that of the firstregion 22 p and that of the second region 22 q. The first region 22 p,the second region 22 q, and the third region 22 r are arranged in thisorder from the downstream side toward the upstream side with respect tothe direction of flow. The first region 22 p is arranged on the sidecloser to the second end portion 21 f. The second region 22 q isarranged between the first region 22 p and the third region 22 r in theaxial direction. The third region 22 r is arranged on a side closer tothe first end portion 21 e. That is, the third region 22 r is arrangedon a side of the second region 22 q closer to the second shaft portion21B.

One of the pair of communicating holes 23 which lies on the upstreamside with respect to the direction of flow is arranged to open in thethird region 22 r. Meanwhile, another one of the pair of communicatingholes 23, which lies on the downstream side with respect to thedirection of flow, is arranged to open in the second region 22 q.

In addition, an inner circumferential surface of the first hollowportion 22A includes a first shoulder surface 22 s arranged between thefirst region 22 p and the second region 22 q, and a second shouldersurface (i.e., a shoulder surface) 22 t arranged between the secondregion 22 q and the third region 22 r. Each of the first shouldersurface 22 s and the second shoulder surface 22 t is arranged to facetoward the second shaft portion 21B. In addition, each of the firstshoulder surface 22 s and the second shoulder surface 22 t is arrangedto slant toward the upstream side with respect to the direction of flowas it extends radially outward.

The third end portion 21 g of the second shaft portion 21B is insertedinto the third region 22 r of the first shaft portion 21A. Femalesplines 22 e are arranged at the third region 22 r. Meanwhile, malesplines 22 g are defined in an outer circumferential surface of thethird end portion 21 g of the second shaft portion 21B. The femalesplines 22 e and the male splines 22 g are fitted to each other. Thefirst shaft portion 21A and the second shaft portion 21B are thusconnected to each other.

A gap is arranged between the second shoulder surface 22 t and an endsurface (i.e., an end surface of the third end portion 21 g) of thesecond shaft portion 21B which faces toward the first shaft portion 21A.The gap between the second shoulder surface 22 t and the end surface ofthe third end portion 21 g defines a recessed groove 22 u in the innercircumferential surface of the hollow portion 22. That is, the recessedgroove 22 u, which is arranged to extend along a circumferentialdirection, is defined in the inner circumferential surface of the hollowportion 22, and the recessed groove 22 u is defined by the end surfaceof the third end portion 21 g of the second shaft portion 21B, an innercircumferential surface of the third region 22 r, and the secondshoulder surface 22 t.

The one of the pair of communicating holes 23 which is arranged on theupstream side with respect to the direction of flow of the oil O isarranged to open into the hollow portion 22 at the recessed groove 22 u.Rotation of the shaft 21 applies a centrifugal force to the oil O fedinto the hollow portion 22. Since the recessed groove 22 u is defined inthe inner circumferential surface of the hollow portion 22, thecentrifugal force causes a portion of the oil O to be gathered in therecessed groove 22 u. According to the present embodiment, the openingof the communicating hole 23 at the recessed groove 22 u allows theportion of the oil O gathered in the recessed groove 22 u to beefficiently led into the communicating hole 23.

According to the present embodiment, the gap at a joint between thefirst shaft portion 21A and the second shaft portion 21B can be used asthe recessed groove 22 u to gather the oil O. This eliminates the needto perform a special process to define the recessed groove 22 u togather the oil O.

In the case where a plurality of communicating holes 23 are arrangedalong the axial direction, there is a tendency for the oil O to moreeasily flow into the communicating hole 23 arranged on the downstreamside with respect to the direction of flow of the oil O, which may causean insufficiency in the amount of a portion of the oil O which flowsinto the communicating hole 23 on the upstream side with respect to thedirection of flow of the oil O. According to the present embodiment, theopening of the communicating hole 23 on the upstream side with respectto the direction of flow at the recessed groove 22 u enables the oil Oto sufficiently flow into the communicating hole 23 on the upstream sidewith respect to the direction of flow.

According to the present embodiment, the diameter of the hollow portion22 is arranged to decrease in a stepwise manner from the upstream sidetoward the downstream side with respect to the direction of flow. Thisarrangement makes it easier for the oil O to spread through the hollowportion 22 from the upstream side to the downstream side. In addition,the upstream one of the pair of communicating holes 23 is arranged to beopen at the third region 22 r, while the other, downstream communicatinghole 23 is arranged to be open at the second region 22 q. That is, anopening of the downstream communicating hole 23 is defined at a regionat which the diameter of the hollow portion 22 is smaller than at aregion at which an opening of the upstream communicating hole 23 isdefined. Accordingly, a sufficient amount of the oil O can be caused toflow into the communicating hole 23 arranged on the downstream side aswell.

A portion of each female spline 22 e is positioned at the gap betweenthe second shoulder surface 22 t and the end surface of the third endportion 21 g. Accordingly, in the inner circumferential surface of thehollow portion 22, projections and recesses are arranged along thecircumferential direction owing to the female splines 22 e. In the casewhere the hollow portion has a circular cross-section centered on themotor axis, the rotation of the shaft may not apply a centrifugal forceto the oil O with the oil O in the hollow portion failing to properlyrotate with respect to the shaft. In contrast, provision of theprojections and recesses arranged along the circumferential direction inthe hollow portion 22 enables the rotation of the shaft 21 to cause theoil O to rotate and to apply a centrifugal force to the oil O in thehollow portion 22. This enables the oil O to be smoothly led into thecommunicating holes 23.

According to the present embodiment, the outer circumferential surfaceof the second shaft portion 21B and the inner circumferential surface ofthe third region 22 r include splines (i.e., the male splines 22 g andthe female splines 22 e) that are spline-fitted to each other. Inaddition, a portion of each spline (i.e., each female spline 22 e) ofthe third region 22 r is positioned in the recessed groove 22 u.Accordingly, the female splines 22 e, which are used for the fitting,can be employed to apply a centrifugal force to the oil O in the hollowportion 22. This eliminates the need to process the innercircumferential surface of the hollow portion 22 to define projectionsand recesses therein to apply a centrifugal force to the oil O.

The rotor core 24 is defined by laminated silicon steel sheets. Therotor core 24 is a columnar body arranged to extend along the axialdirection. The rotor core 24 includes a pair of axial end surfaces 24 aarranged to face away from each other in the axial direction, and anouter circumferential surface 24 b arranged to face radially outward.

The rotor core 24, together with the pair of end plates 26, is heldbetween the nut 29 and the collar portion 21 c. The washer 28 isinterposed between the nut 29 and an adjacent one of the end plates 26.

The rotor core 24 includes a plurality of magnet holding holes 24 d, aplurality of core through holes 24 e, and one fitting hole 24 c, whichis positioned in a center of the rotor core 24 when viewed in the axialdirection, and which is arranged to pass through the rotor core 24 alongthe axial direction. Each of the fitting hole 24 c, the magnet holdingholes 24 d, and the core through holes 24 e is arranged to open in thepair of axial end surfaces 24 a.

The fitting hole 24 c is circular, and is centered on the motor axis J2.The shaft 21 is inserted through and fitted in the fitting hole 24 c.Accordingly, the rotor core 24 surrounds the shaft 21 from radiallyoutside. The fitting of the shaft 21 in the fitting hole 24 c is a loosefitting. This contributes to preventing the rotor core 24 from beingdeformed due to the fitting of the shaft 21. An inner circumferentialsurface of the fitting hole 24 c includes a projection (not shown)arranged to project radially inward. This projection is fitted into akey groove (not shown) defined in the outer circumferential surface ofthe shaft 21. This prevents a relative rotation between the rotor core24 and the shaft 21.

The plurality of core through holes 24 e are arranged along thecircumferential direction. The core through holes 24 e are arrangedradially inward of the magnet holding holes 24 d. Each core through hole24 e plays a role of passing the oil O between the pair of axial endsurfaces 24 a.

The plurality of magnet holding holes 24 d are arranged along thecircumferential direction. The rotor magnets 25 are inserted in themagnet holding holes 24 d. Each magnet holding hole 24 d is arranged tohold the corresponding rotor magnet 25. That is, the rotor 20 accordingto the present embodiment is of an IPM (Interior Permanent Magnet) type,in which the rotor magnets 25 are embedded in the rotor core 24.

Each rotor magnet 25 is a permanent magnet. The plurality of rotormagnets 25 are inserted into the respective magnet holding holes 24 darranged in the circumferential direction to be fixed to the rotor core24. The plurality of rotor magnets 25 are arranged along thecircumferential direction.

FIG. 6 is a plan of the end plate 26. FIG. 7 is a sectional view of theend plate 26 taken along line VII-VII in FIG. 6. Note that, in each ofFIGS. 6 and 7, other members of the motor assembly 1 are represented byimaginary lines.

Referring to FIG. 6, the end plate 26 is circular in plan view. The endplate 26 is a plate made of a metal. The end plate 26 includes acircular central hole 26 i arranged to pass therethrough along the axialdirection. An inner circumferential surface of the central hole 26 iincludes a key portion 26 q. The key portion 26 q is fitted into a keygroove 21 k defined in the shaft 21. The end plate 26 and the shaft 21are prevented by the fitting of the key portion 26 q into the key groove21 k from rotating relative to each other.

Referring to FIG. 5, each end plate 26 includes a first surface 26 a anda second surface 26 b. The first surface 26 a is arranged opposite tothe corresponding axial end surface 24 a of the rotor core 24. Thesecond surface 26 b is arranged to face away from the first surface 26a.

The pair of end plates 26 are arranged on opposite axial sides of therotor core 24. Each of the pair of end plates 26 is arranged to be incontact with a corresponding one of the pair of axial end surfaces 24 aof the rotor core 24. One of the pair of end plates 26 (i.e., a firstend plate 26A) is arranged between the collar portion 21 c and one ofthe axial end surfaces 24 a of the rotor core 24. Another one of thepair of end plates 26 (i.e., a second end plate 26B) is arranged betweenthe washer 28 and another one of the axial end surfaces 24 a of therotor core 24. Each end plate 26 is arranged to be in contact with thecorresponding axial end surface 24 a at the first surface 26 a. Inaddition, each end plate 26 is arranged to be in contact with the collarportion 21 c or the washer 28 at the second surface 26 b.

According to the present embodiment, the rotor core 24 and the pair ofend plates 26 are held between the collar portion 21 c and the nut 29.Thus, the pair of end plates 26 are pressed against the axial endsurfaces 24 a of the rotor core 24 from both axial sides. Friction isgenerated at a junction between the first surface 26 a of each end plate26 and the corresponding axial end surface 24 a of the rotor core 24, sothat a relative rotation between the rotor core 24 and the shaft 21 canbe prevented.

If the rotor core and the shaft are fixed to each other through pressfitting, the rotor core will be deformed to affect a magnetic pathpassing through the rotor core, resulting in an increased core loss. Inparticular, in the case of a motor designed to drive a vehicle as in thecase of the present embodiment, a large press-fitting interference needsto be secured because of a large driving force, and a large core losstends to occur in the rotor core. According to the present embodiment,the rotor core 24 is fixed to the shaft 21 through the end plates 26.This makes it possible to fit the shaft 21 in the fitting hole 24 c ofthe rotor core 24 through loose fitting, which contributes to preventingor minimizing a deformation of the rotor core 24, and thus increasingthe efficiency of the motor 2.

Referring to FIG. 7, the first surface 26 a includes a recessed portion26 f and a slanting surface 26 e arranged to surround the recessedportion 26 f from radially outside. The recessed portion 26 f iscircular and is centered on the motor axis J2 in plan view. The recessedportion 26 f includes a “recessed portion bottom surface” 26 g and a“recessed portion inner circumferential surface” 26 h. The recessedportion bottom surface 26 g is a flat surface perpendicular to the motoraxis J2. The recessed portion inner circumferential surface 26 h isarranged between the recessed portion bottom surface 26 g and theslanting surface 26 e. The recessed portion inner circumferentialsurface 26 h is arranged to slant in such a direction as to decrease thedepth of the recessed portion 26 f as it extends radially outward from aradially inner end thereof. A gap is arranged between the recessedportion 26 f and the corresponding axial end surface 24 a of the rotorcore 24. The oil O is gathered in this gap to cool the correspondingaxial end surface 24 a of the rotor core 24.

The slanting surface 26 e is arranged in a region positioned mostradially outward in the first surface 26 a, and is arranged to extendalong the circumferential direction. The slanting surface 26 e isarranged to slant toward the rotor core 24 at an inclination angle θ asit extends radially outward. Note here that the inclination angle θrefers to an angle defined by the slanting surface 26 e with a planeperpendicular to the motor axis J2.

The end plate 26 is arranged to be in contact with the correspondingaxial end surface 24 a of the rotor core 24 at the slanting surface 26 ein the first surface 26 a. Since the slanting surface 26 e slants towardthe rotor core 24 as it extends radially outward, the slanting surface26 e is in contact with the corresponding axial end surface 24 a at aradially outermost region. This allows friction generated by the contactbetween the slanting surface 26 e and the axial end surface 24 a to begenerated as radially outward as possible. In addition, a normal stressbetween the slanting surface 26 e and the axial end surface 24 a can bemade progressively greater in the radially outward direction. Thus, thevalue of a maximum static friction can be made progressively greater inthe radially outward direction. A holding torque for preventing arelative rotation between the end plate 26 and the rotor core 24 isproportional to the distance from the rotation axis and friction.Therefore, according to the present embodiment, the holding torque forpreventing a relative rotation between the end plate 26 and the rotorcore 24 can be increased, making it possible to securely hold the rotorcore 24 with respect to the end plate 26. To achieve this effect, it ispreferable that the inclination angle θ of the slanting surface 26 e isin the range of 0.1° to 5° both inclusive.

In addition, the end plate 26 according to the present embodiment isarranged to be in contact with the corresponding axial end surface 24 aof the rotor core 24 at the slanting surface 26 e. This arrangementcontributes to stabilizing points of contact between the end plate 26and the rotor core 24. Accordingly, variations in torque transferredbetween the end plate 26 and the rotor core 24 can be minimized tosecurely fix the rotor core 24 with respect to the shaft 21.

In addition, according to the present embodiment, provision of theslanting surface 26 e in the end plate 26 enables the end plate 26 to besecurely brought into contact with the axial end surface 24 a of therotor core 24 even if there are variations in flatness of the junctionbetween the end plate 26 and the axial end surface 24 a. As will bedescribed later, an oil flow passage 26 t (see FIG. 5) is arrangedradially inside of the slanting surface 26 e. An intrusion of an oilinto a gap between a rotor core and a stator generally causes areduction in rotation efficiency of the rotor core. The contact of theslanting surface 26 e with the axial end surface 24 a of the rotor core24 contributes to preventing the oil O in the oil flow passage 26 t fromintruding into a gap between the stator 30 and the outer circumferentialsurface 24 b of the rotor core 24 through a gap between the end plate 26and the rotor core 24.

Note that the slanting surface 26 e may alternatively be arranged tovary in the inclination angle as it extends radially outward. Also notethat the slanting surface 26 e may alternatively be a curved surfacethat varies in the inclination angle as it extends radially outward.

Referring to FIG. 5, the slanting surface 26 e is arranged to close anopening of each magnet holding hole 24 d of the rotor core 24. Thisarrangement contributes to preventing each rotor magnet 25 held in thecorresponding magnet holding hole 24 d from protruding from the openingof the corresponding magnet holding hole 24 d. This in turn contributesto preventing a portion of any rotor magnet 25 from intruding into adrive portion within a recessed housing portion.

Referring to FIG. 7, the second surface 26 b includes a flat portion 26c and a chamfer portion 26 d arranged at an outer edge of the flatportion 26 c. The flat portion 26 c is perpendicular to the motor axisJ2. The chamfer portion 26 d is arranged to slant toward the firstsurface 26 a as it extends radially outward.

Referring to FIG. 5, the end plate 26 includes two sets each of which ismade up of a plate through hole 26 p, a first recessed groove (i.e., afirst recessed portion) 26 j, and a second recessed groove (i.e., asecond recessed portion) 26 k. While one of the two sets, each of whichis made up of the plate through hole 26 p, the first recessed groove 26j, and the second recessed groove 26 k, will be described below, it isto be noted that the other set has the same configuration.

The plate through hole 26 p is arranged to extend along the axialdirection. The first recessed groove 26 j is arranged in the firstsurface 26 a. The first recessed groove 26 j is arranged to extendradially inward from an opening of the plate through hole 26 p. Thefirst recessed groove 26 j is arranged to open radially inward at theinner circumferential surface of the central hole 26 i. The secondrecessed groove 26 k is arranged in the second surface 26 b. The secondrecessed groove 26 k is arranged to extend radially outward from anopening of the plate through hole 26 p. The second recessed groove 26 kis arranged to open radially outward at the chamfer portion 26 d.

An axially-facing opening of the first recessed groove 26 j of the endplate 26 is covered with the corresponding axial end surface 24 a of therotor core 24. In addition, a radial opening of the first recessedgroove 26 j is connected to the corresponding communicating hole 23 ofthe shaft 21.

A portion of the oil O which has been fed into the hollow portion 22 ofthe shaft 21 flows radially outward through the communicating hole 23.In addition, the oil O flows into the first recessed groove 26 j througha radially outer opening of the communicating hole 23. Further, the oilO flows toward the first surface 26 a and the second surface 26 bthrough the plate through hole 26 p, and is discharged out of the rotor20 through the second recessed groove 26 k. Referring to FIG. 4, thecoil ends 31 a of the stator 30 lie radially outside of the end plate26. The oil O discharged out of the rotor 20 is fed to the coil ends 31a to cool the coil ends 31 a.

The first recessed groove 26 j, the plate through hole 26 p, and thesecond recessed groove 26 k of the end plate 26 function as the oil flowpassage 26 t. In other words, the oil flow passage 26 t is defined bythe first recessed groove 26 j, the plate through hole 26 p, and thesecond recessed groove 26 k. The oil flow passage 26 t, which isarranged to extend along a radial direction to open into thecommunicating hole 23, is defined in each of the pair of end plates 26.

In the end plate 26 according to the present embodiment, the platethrough hole 26 p, the first recessed groove 26 j, and the secondrecessed groove 26 k together define the oil flow passage 26 t.Therefore, according to the present embodiment, the oil flow passage 26t can be defined by an inexpensive part (i.e., the end plate 26)produced by a molding process.

Each first recessed groove 26 j of each of the pair of end plates 26 isarranged to be in communication with one of the core through holes 24 e.That is, each core through hole 24 e is arranged to connect thecorresponding first recessed grooves 26 j of the pair of end plates 26to each other. In other words, each core through hole 24 e is arrangedto connect the corresponding oil flow passages 26 t of the pair of endplates 26 to each other. In addition, at least a portion of an openingof each core through hole is arranged radially outward of thecorresponding plate through hole 26 p.

According to the present embodiment, each core through hole 24 e isarranged to connect the corresponding first recessed grooves 26 j of thepair of end plates 26 to each other, and this arrangement enables aportion of the oil O passing through each first recessed groove 26 j toflow into the core through hole 24 e. Thus, the oil O in the corethrough hole 24 e can be used to cool the rotor core 24 from inside. Inaddition, the rotor magnets 25 held on the rotor core 24 can be cooledthrough the rotor core 24.

According to the present embodiment, openings of each core through hole24 e are arranged radially outward of the corresponding plate throughholes 26 p of the pair of end plates 26. This arrangement enables theoil O to be gathered in the core through hole 24 e through a centrifugalforce of the rotor 20, and enables the oil O to be fed from the corethrough hole 24 e to the corresponding first recessed grooves 26 j ofthe end plates 26 on both sides. In addition, when there is not enoughof the oil O in the corresponding first recessed groove 26 j of one ofthe pair of end plates 26, the oil O can be fed from the other firstrecessed groove 26 j through the core through hole 24 e. Accordingly,the oil O can be discharged out of both the end plates 26 onto the coilends 31 a in substantially equal amounts, enabling stable cooling of thecoils 31.

Referring to FIG. 5, one of the pair of end plates 26 which is heldbetween the collar portion 21 c and the rotor core 24 is referred to asthe first end plate 26A, while the other end plate 26, which is heldbetween the nut 29 and the rotor core 24, is referred to as the secondend plate 26B.

In the first end plate 26A, a radially inner portion of each platethrough hole 26 p is covered with the collar portion 21 c. In addition,in the first end plate 26A, an axially-facing opening of each secondrecessed groove 26 k is arranged to face on an axial outside in itsentirety. In other words, in the first end plate 26A, the axially-facingopening of each second recessed groove 26 k is exposed in its entiretywhen viewed in the axial direction. That is, each second recessed groove26 k of the first end plate 26A is arranged to be in communication withthe outside through the axially-facing opening. In the first end plate26A, a portion of each plate through hole 26 p and the entireaxially-facing opening of each second recessed groove 26 k function as afirst open portion 26 s free from the collar portion 21 c. In the firstend plate 26A, a portion of the oil O which has passed through eachplate through hole 26 p is discharged through the first open portion 26s.

The washer 28 is interposed between the second end plate 26B and the nut29. In the second end plate 26B, each plate through hole 26 p and aradially inner portion of an axially-facing opening of each secondrecessed groove 26 k are covered with the washer 28. The portion of theaxially-facing opening of each second recessed groove 26 k which iscovered with the washer 28 is referred to as a covered portion, while aportion of the axially-facing opening of each second recessed groove 26k which is not covered with the washer 28 is referred to as an openportion. That is, in the second end plate 26B, the axially-facingopening of each second recessed groove 26 k includes a covered portionbeing covered with the washer 28, and a second open portion 26 r notbeing covered with the washer 28. Each second recessed groove 26 k ofthe second end plate 26B is arranged to face on an axial outside at thesecond open portion 26 r, which is arranged at a radially outer endportion of the second recessed groove 26 k. In other words, each secondrecessed groove 26 k of the second end plate 26B is exposed at thesecond open portion 26 r when viewed in the axial direction. That is,each second recessed groove 26 k of the second end plate 26B is arrangedto be in communication with the outside through the second open portion26 r. The second open portion 26 r is positioned at the radially outerend portion of the second recessed groove 26 k. In the second end plate26B, a portion of the oil O which has passed through each plate throughhole 26 p is discharged through the second open portion 26 r.

In each of the first end plate 26A and the second end plate 26Baccording to the present embodiment, the second recessed grooves 26 kare arranged in the second surface 26 b, and this enables a portion ofthe oil O which flows toward the second surface 26 b through each platethrough hole 26 p to travel radially outward along the correspondingsecond recessed groove 26 k. This makes it possible to stably pass theoil O to the second open portion 26 r, making it possible to stably feedthe oil O to the coil ends 31 a of the stator 30.

According to the present embodiment, for the second recessed grooves 26k of each of the first end plate 26A and the second end plate 26B, thecollar portion 21 c or the washer 28 functions as a cover portionarranged to cover an axial opening. That is, the rotor 20 includes apair of cover portions (i.e., the collar portion 21 c and the washer 28)arranged at axial end portions of the rotor core 24 with the end plate26 intervening between each cover portion and the rotor core 24. Each ofthe cover portions (i.e., the collar portion 21 c and the washer 28),externally covering an axially-facing opening of each plate through hole26 p, leads a portion of the oil O which flows toward the second surface26 b through the plate through hole 26 p to flow along the correspondingsecond recessed groove 26 k. According to the present embodiment, eachof the cover portions (i.e., the collar portion 21 c and the washer 28)controls the behavior of the oil O to prevent the oil O from intrudinginto the gap between the rotor core 24 and the stator 30.

In the second end plate 26B according to the present embodiment, theaxially-facing opening of each second recessed groove 26 k is partlycovered with the washer 28, and faces on the axial outside at the secondopen portion 26 r. That is, at a region leading to the second openportion 26 r of the second recessed groove 26 k, the oil O does not flowout in the axial direction, so that the oil O can be securelytransferred to the second open portion 26 r. Thus, the oil O can bestably discharged through the second open portion 26 r, and the oil Ocan be stably fed to the coil ends 31 a.

According to the present embodiment, the second recessed groove 26 k isarranged to face axially on the axial outside at the second open portion26 r, which is positioned at a radial end portion. Accordingly, aportion of the oil O which has passed through the second recessed groove26 k can be scattered in the axial direction through the second openportion 26 r. Thus, the oil O can be scattered toward the coil ends 31a, which project in the axial direction relative to an end portion ofthe rotor core 24, to effectively cool the coils 31 of the coil ends 31a.

In the first end plate 26A according to the present embodiment, thefirst open portion 26 s is arranged to extend over a portion of thecorresponding plate through hole 26 p and the entire axially-facingopening. Note, however, that the collar portion 21 c may alternativelybe arranged to cover a portion of the axially-facing opening of eachsecond recessed groove 26 k as indicated by imaginary lines in FIG. 5.In this case, the first open portion 26 s of the first end plate 26A ispositioned at a radially outer end portion as is the second open portion26 r of the second end plate 26B, and can achieve an effect similar tothat of the second open portion 26 r.

In the present embodiment, the first recessed grooves 26 j and thesecond recessed grooves 26 k, each of which is in the shape of a groove,are arranged in each end plate 26. Note, however, that recessed portionsthat are not in the shape of a groove may alternatively be arrangedtherein to achieve the above-described effect to some degree. Note that,when each of the first recessed grooves 26 j and the second recessedgrooves 26 k is arranged to extend along a radial direction, the oil Ocan be smoothly led along the radial direction.

FIG. 8 is a sectional view of an end plate 126 according to a firstmodification, which can be adopted in the present embodiment. Note that,in the following description, elements that have their equivalents inthe above-described embodiment are denoted by the same referencecharacters as those of their equivalents in the above-describedembodiment.

Similarly to the end plate 26 according to the above-describedembodiment, the end plate 126 according to the first modificationincludes a first surface 126 a arranged opposite to the rotor core 24,and a second surface 126 b arranged to face away from the first surface126 a. In addition, a pair of plate through holes 126 p, a pair of firstrecessed grooves 126 j, and a pair of second recessed grooves 126 k arearranged in the end plate 126. Each plate through hole 126 p is arrangedto extend in the axial direction. Each first recessed groove 126 j isarranged in the first surface 126 a. Each first recessed groove 126 j isarranged to extend radially inward from the corresponding plate throughhole 126 p. Each second recessed groove 126 k is arranged in the secondsurface 126 b. Each second recessed groove 126 k is arranged to extendradially outward from the corresponding plate through hole 126 p. Anaxially-facing opening of each second recessed groove 126 k is partlycovered with a cover portion 128, and is arranged to face on an axialoutside at an open portion 126 r. Note here that the cover portion 128is the washer 28 or the collar portion 21 c (see FIG. 5).

In the present modification, a bottom portion of each second recessedgroove 126 k includes a slanting surface 126 u arranged to decrease thedepth of the second recessed groove 126 k with decreasing distance froma radially outer end. The slanting surface 126 u is arranged to overlapwith the open portion 126 r when viewed in the axial direction.According to the present modification, provision of the slanting surface126 u in the second recessed groove 126 k adds an axial component to aflow of the oil O. Thus, the oil O can be scattered in the axialdirection, and the oil O can be effectively scattered toward the coilends 31 a, which project in the axial direction relative to an endportion of the rotor core 24.

FIG. 9 is a plan of an end plate 226 according to a second modification,which can be adopted in the present embodiment. Note that, in thefollowing description, elements that have their equivalents in theabove-described embodiment are denoted by the same reference charactersas those of their equivalents in the above-described embodiment.

Similarly to the end plate 26 according to the above-describedembodiment, the end plate 226 according to the second modificationincludes a first surface 226 a and a second surface 226 b arranged toface away from the first surface 226 a. In addition, the end plate 226includes a pair of plate through holes 226 p, a pair of first recessedgrooves 226 j, and a pair of second recessed grooves 226 k. Each platethrough hole 226 p is arranged to extend in the axial direction. Eachfirst recessed groove 226 j is arranged in the first surface 226 a. Eachfirst recessed groove 226 j is arranged to extend radially inward fromthe corresponding plate through hole 226 p. Each second recessed groove226 k is arranged in the second surface 226 b. Each second recessedgroove 226 k is arranged to extend radially outward from thecorresponding plate through hole 226 p. An axially-facing opening ofeach second recessed groove 226 k is partly covered with a cover portion228, and is arranged to face on an axial outside at an open portion 226r. Note here that the cover portion 228 is the washer 28 or the collarportion 21 c (see FIG. 5).

Each second recessed groove 226 k is a groove arranged to extend along aradial direction. In addition, a direction in which the second recessedgroove 226 k extends when viewed in the axial direction is arranged toslant with respect to the radial direction. Further, the second recessedgroove 226 k is arranged to curve so as to increase an inclination anglethereof with respect to the radial direction as it extends radiallyoutward. According to the present modification, the slanting of thesecond recessed groove 226 k with respect to the radial direction makesit possible for a wall surface of the slanting second recessed groove226 k to apply a centrifugal force to a portion of the oil O whichpasses through the second recessed groove 226 k. This will increase thespeed at which the oil O is scattered from the open portion 226 r, andcan ensure that the oil O will reach the coil ends 31 a even when thecoil ends 31 a are at a distance.

The pair of second recessed grooves 226 k according to the presentmodification are arranged to have different shapes when viewed in theaxial direction. One of the pair of second recessed grooves 226 k, asecond recessed groove 226 kA, is arranged to have a smaller curvaturewhen viewed in the axial direction, and have smaller inclination angleswith respect to the radial direction, than another one of the secondrecessed grooves 226 k, a second recessed groove 226 kB. That is,according to the present embodiment, a direction in which the groove ofeach of the plurality of second recessed grooves 226 kA and 226 kBextends when viewed in the axial direction is arranged to have adifferent angle with respect to the radial direction. Accordingly,centrifugal forces applied by the pair of second recessed grooves 226 kAand 226 kB to the oil O have mutually different magnitudes. A portion ofthe oil O which is scattered from the other second recessed groove 226kB has a higher speed and is scattered to a farther region than aportion of the oil O which is scattered from the one second recessedgroove 226 kA. That is, according to the present modification, the oil Ocan be scattered to mutually different regions through the plurality ofsecond recessed grooves 226 kA and 226 kB, so that the oil O can reach awider range over the coil ends 31 a.

Referring to FIG. 1, the oil passage 90 is arranged inside of thehousing 6, that is, in the housing space 80. The oil passage 90 isarranged to extend over both the motor chamber 81 and the gear chamber82 of the housing space 80. The oil passage 90 is a channel of the oil Oalong which the oil O is fed from the oil pool P (i.e., the lower regionof the housing space 80) through the motor 2 back to the oil pool P. Theoil passage 90 includes the first oil passage (i.e., an oil passage) 91,which is arranged to pass through an inside of the motor 2, and thesecond oil passage (i.e., an oil passage) 92, which is arranged to passthrough an outside of the motor 2. The oil O cools the motor 2 from theinside and the outside through the first oil passage 91 and the secondoil passage 92. The oil passage 90 defines an oil cooling mechanism.

Each of the first oil passage 91 and the second oil passage 92 is achannel along which the oil O is fed from the oil pool P to the motor 2and back into the oil pool P. In each of the first oil passage 91 andthe second oil passage 92, the oil O drips from the motor 2 to begathered in the lower region of the motor chamber 81. The oil O gatheredin the lower region of the motor chamber 81 is transferred to the lowerregion of the gear chamber 82 (i.e., the oil pool P) through thepartition opening 68.

A cooler 97 is arranged in the channel of the second oil passage 92 tocool the oil O. A portion of the oil O which passes through the secondoil passage 92 and is cooled by the cooler 97 joins a portion of the oilO which passes through the first oil passage 91 at the oil pool P. Atthe oil pool P, portions of the oil O which have passed through thefirst oil passage 91 and the second oil passage 92 mix with each other,so that heat is exchanged therebetween. Thus, a cooling effect producedby the cooler 97 arranged in the channel of the second oil passage 92will have an influence on the portion of the oil O which passes throughthe first oil passage 91. According to the present embodiment, thesingle cooler 97, which is arranged in one of the first oil passage 91and the second oil passage 92, is used to cool the oil O in both the oilpassages.

A cooler is generally arranged in a flow passage through which a liquidsteadily flows. It is conceivable to arrange a cooler in each of flowpassages included in the two oil passages to cool the two oil passages.This arrangement requires use of two coolers, and leads to an increasedcost. It is also conceivable to arrange a flow passage in a region wherethe two oil passages join, and install a cooler in this flow passage, tocool the two oil passages. This arrangement requires the flow passage tobe arranged in the junction region, which will require complicatedstructures of flow passages in the oil passage, resulting in a highcost.

According to the present embodiment, the cooler is arranged in only thesecond oil passage 92, and the first oil passage 91 can be indirectlycooled by the mixing of the portions of the oil O which pass through thefirst oil passage 91 and the second oil passage 92 at the oil pool P.This allows the oil O in each of the first oil passage 91 and the secondoil passage 92 to be cooled by the single cooler 97 without the need forcomplicated structures of flow passages in the oil passage 90.

Note that the above effect can be achieved when the cooler 97 to coolthe oil O is arranged in one of the first oil passage 91 and the secondoil passage 92, and portions of the oil O which flow through the firstoil passage 91 and the second oil passage 92 join at the oil pool P.

Heat of the oil O is mainly dissipated through the cooler 97. Inaddition, a portion of the heat of the oil O is dissipated through thehousing 6 due to a contact of the oil O with an inner surface of thehousing 6. Note that, as illustrated in FIG. 1, a heat sink portion 6 bhaving projections and recesses may be arranged on an outer surface ofthe housing 6. The heat sink portion 6 b will facilitate the cooling ofthe motor 2 through the housing 6.

The oil O is scraped up by the differential 5 from the oil pool P, andis led into an interior of the rotor 20 through the first oil passage91. A centrifugal force caused by the rotation of the rotor 20 isapplied to the oil O in the interior of the rotor 20. The oil O is thusspread evenly toward the stator 30, which is arranged to surround therotor 20 from radially outside, to cool the stator 30.

The first oil passage 91 includes a scraping-up channel 91 a, a shaftfeed channel (i.e., an oil flow passage) 91 b, an intra-shaft channel 91c, and an intra-rotor channel 91 d. In addition, the first reservoir 93is arranged in the channel of the first oil passage 91. The firstreservoir 93 is arranged in the housing space 80 (particularly, in thegear chamber 82).

The scraping-up channel 91 a is a channel along which the oil O isscraped up from the oil pool P by rotation of the ring gear 51 of thedifferential 5 to be received by the first reservoir 93 (see FIG. 3).

Referring to FIG. 3, the first reservoir 93 is arranged higher than eachof the motor axis J2, the intermediate axis J4, and the differentialaxis J5 in the vertical direction. The first reservoir 93 is arrangedbetween the intermediate axis J4 and the differential axis J5 in thefront-rear direction of the vehicle (i.e., a horizontal direction andthe x-axis direction). The first reservoir 93 is arranged between themotor axis J2 and the differential axis J5 in the front-rear directionof the vehicle (i.e., the horizontal direction and the x-axisdirection). The first reservoir 93 is arranged at a side of the firstgear 41. The first reservoir 93 is arranged to open upward.

In the present specification, the term “reservoir” refers to a structurethat has a function of storing the oil without a steady flow of a liquidtraveling in one direction. A “reservoir” differs from a “flow passage”in that there is no steady flow of a liquid. The first reservoir 93, asecond reservoir 98, and an auxiliary reservoir 95 are arranged in thehousing space 80 of the motor assembly 1 according to the presentembodiment.

In the present embodiment, the differential axis J5, about which thering gear 51 is arranged to rotate, is arranged on a rear side of thereduction gear 4 with respect to the vehicle. When the vehicle istraveling forward, the differential 5 rotates upward in a region on theside opposite to the reduction gear 4. A portion of the oil O which isscraped up by the ring gear 51 of the differential 5 passes on the sideaway from the reduction gear 4, is poured upon the first reservoir 93,and is gathered in the first reservoir 93. That is, the first reservoir93 receives the portion of the oil O which has been scraped up by thering gear 51. In addition, when a liquid surface of the oil pool P lieshigh, such as immediately after the motor 2 is driven, each of thesecond gear 42 and the third gear 43 is in contact with the oil O in theoil pool P, and scrapes up the oil O. In this case, the first reservoir93 receives portions of the oil O which have been scraped up by thesecond gear 42 and the third gear 43 in addition to the portion of theoil O which has been scraped up by the ring gear 51.

The housing 6 includes a gear chamber ceiling portion (i.e., a ceilingportion) 64 arranged to define an upper wall of the gear chamber 82. Thegear chamber ceiling portion 64 is arranged above the reduction gear 4and the differential 5. Here, an imaginary line (i.e., a third linesegment described below) L3, which imaginarily joins the motor axis J2and the differential axis J5 when viewed in the axial direction of themotor axis J2, is defined. The gear chamber ceiling portion 64 isarranged to be substantially parallel to the imaginary line L3.Arranging the gear chamber ceiling portion 64 to be substantiallyparallel to the imaginary line L3 enables the oil O to efficiently reachthe first gear 41, which rotates about the motor axis J, while ensuringa sufficient size of a region where a portion of the oil O which isscraped up by the ring gear 51 and is scattered in a direction in whichthe imaginary line L3 extends passes. In addition, arranging the gearchamber ceiling portion 64 to be substantially parallel to the imaginaryline L3 contributes to preventing an excessively large verticaldimension of the housing 6.

Note that it is assumed here that the gear chamber ceiling portion 64being “substantially parallel to” the imaginary line L3 means that anangle defined by the gear chamber ceiling portion 64 with the imaginaryline L3 is 10° or less. In the case where the gear chamber ceilingportion 64 is arranged to curve, an angle defined by a tangent to thecurved line at every point with the imaginary line L3 is 10° or less.

In addition, it is preferable that the gear chamber ceiling portion 64is arranged to approach the imaginary line L3 as it extends from a sideon which the differential axis J5 lies toward a side on which the motoraxis J2 lies, as long as the aforementioned angle is 10° or less. Thiswill lead to a reduced size of the housing 6.

In addition, the gear chamber ceiling portion 64 is a curved surfacethat slightly curves in such a direction as to approach the imaginaryline L3 as it extends from the side on which the differential axis J5lies toward the side on which the motor axis J2 lies. The curved shapeof the gear chamber ceiling portion 64 substantially matches a paraboladrawn by the portion of the oil O which is scraped up by the ring gear51, or the gear chamber ceiling portion 64 is a curved surface thatbecomes slightly more distant from the ring gear 51. A portion of theoil O scraped up by the ring gear 51 directly reaches the firstreservoir 93. Another portion of the oil O scraped up by the ring gear51 reaches the first reservoir 93, traveling on and along the gearchamber ceiling portion 64 of the housing 6. That is, the gear chamberceiling portion 64 plays the role of leading the oil O to the firstreservoir 93.

The gear chamber ceiling portion 64 includes a protruding portion 65arranged to protrude downward. The protruding portion 65 is arranged onthe upper side of the first reservoir 93. The portion of the oil O whichtravels on and along the gear chamber ceiling portion 64 forms a bigdrop at a lower end of the protruding portion 65, and the big drop fallsdownward to be gathered in the first reservoir 93. That is, theprotruding portion 65 leads the portion of the oil O which travels onand along the gear chamber ceiling portion 64 to the first reservoir 93.

In the present embodiment, the motor housing portion 61 and the gearhousing portion 62 are fixed to each other through bolts 67. Theprotruding portion 65 is defined using an increased thickness portionaround a screw hole into which one of the bolts 67 is inserted at thegear chamber ceiling portion 64. Note that, in FIG. 3, other bolts usedto fix the motor housing portion 61 and the gear housing portion 62 toeach other, and other increased thickness portions around other screwholes, are not shown.

The gear chamber ceiling portion 64 includes a plate-shaped visorportion 66 arranged to extend along the axial direction. The visorportion 66 is arranged to project downward. A lower end of the visorportion 66 is arranged on the upper side of the first reservoir 93. Aportion of the oil O scraped up by the ring gear 51 and scatteredstrikes the visor portion 66, and travels on and along a surface of thevisor portion 66. Similarly, portions of the oil O which are scraped upby the second gear 42 and the third gear 43 to be scattered are receivedby the visor portion 66, and travel on and along the surface of thevisor portion 66. The oil O forms a big drop at the lower end of thevisor portion 66, and the big drop falls downward to be gathered in thefirst reservoir 93. That is, the visor portion 66 leads the oil Oscraped up to the first reservoir 93.

The visor portion 66 is arranged to slant from the side on which thedifferential axis J5 lies toward the side on which the motor axis J2lies as it extends downward from an upper end thereof. The ring gear 51has a diameter greater than that of the second gear 42 and that of thethird gear 43, and therefore causes the oil O to be scattered indirections at a small angle to the horizontal. Arranging the visorportion 66 to slant in the aforementioned direction allows the portionof the oil O which is scattered from the ring gear 51 to be attached tothe surface of the visor portion 66 and fall downward in a smoothmanner.

The first reservoir 93 is arranged directly above the ring gear 51, thesecond gear 42, and the third gear 43. An opening of the first reservoir93 is arranged to overlap with each of the ring gear 51, the second gear42, and the third gear 43 when viewed in the vertical direction. A largeportion of the oil scraped up by any gear is scattered directly upwardof the gear scraping up the oil. Arranging the first reservoir 93directly above each of the ring gear 51, the second gear 42, and thethird gear 43 leads to efficient reception of the oil O scraped up byeach of the gears.

The first reservoir 93 includes a bottom portion 93 a, a first side wallportion 93 b, and a second side wall portion 93 c. Each of the bottomportion 93 a, the first side wall portion 93 b, and the second side wallportion 93 c is arranged to extend along the axial direction betweenwall surfaces of the gear housing portion 62 and the projecting plateportion 61 d of the motor housing portion 61. Each of the first sidewall portion 93 b and the second side wall portion 93 c is arranged toextend upward from the bottom portion 93 a. The first side wall portion93 b defines a wall surface of the first reservoir 93 on the side closerto the differential 5. The second side wall portion 93 c defines a wallsurface of the first reservoir 93 on the side closer to the reductiongear 4. That is, the first side wall portion 93 b is arranged to extendupward from an end portion of the bottom portion 93 a on the side closerto the differential axis J5, while the second side wall portion 93 c isarranged to extend upward from an end portion of the bottom portion 93 aon the side closer to the motor axis J2. The first reservoir 93temporarily stores the oil O in a region surrounded by the bottomportion 93 a, the first side wall portion 93 b, the second side wallportion 93 c, and the wall surfaces of the gear housing portion 62 andthe projecting plate portion 61 d of the motor housing portion 61.

An upper end portion of the first side wall portion 93 b is arrangedlower than an upper end portion of the second side wall portion 93 c.The oil O is scraped up by the differential 5, and is scattered towardthe first reservoir 93 from the side opposite to the reduction gear 4.Due to the upper end portion of the first side wall portion 93 b beingarranged at a lower level, the oil O scraped up by the differential 5can be efficiently stored in the first reservoir 93. In addition, of theoil O scraped up by the ring gear 51 and scattered, a portion whichpasses over the first side wall portion 93 b is allowed to strike thesecond side wall portion 93 c to be led into the first reservoir 93.

The second side wall portion 93 c is arranged to extend obliquely upwardalong a circumferential direction of the first gear 41. That is, thesecond side wall portion 93 c is arranged to slant toward the motor axisJ2 as it extends upward. Thus, the second side wall portion 93 c is ableto receive the oil O scraped up by the differential 5 over a large area.In addition, the second side wall portion 93 c is able to receive dropsof the oil O traveling on and along a ceiling of the housing space 80over a large area.

The shaft feed flow passage 94 is arranged to open into an interior ofthe first reservoir 93 at a boundary between the bottom portion 93 a andthe second side wall portion 93 c. The bottom portion 93 a is arrangedto slightly slant downward as it extends toward the motor axis J2 inplan view. That is, the bottom portion 93 a is arranged to slightlyslant in such a manner that a lower end of the bottom portion 93 a is onthe side closer to the second side wall portion 93 c. Accordingly, withan opening of the shaft feed flow passage 94 being arranged at theboundary between the bottom portion 93 a and the second side wallportion 93 c, the oil O in the first reservoir 93 can be efficiently fedinto the shaft feed flow passage 94.

The shaft feed channel 91 b is arranged to lead the oil O from the firstreservoir 93 to the motor 2. The shaft feed channel 91 b is defined bythe shaft feed flow passage 94. The shaft feed flow passage 94 isarranged to extend from the first reservoir 93 toward an end portion ofthe shaft 21. The shaft feed flow passage 94 is arranged to extend in astraight line. The shaft feed flow passage 94 is arranged to slantdownward as it extends from the first reservoir 93 toward the endportion of the shaft 21. The shaft feed flow passage 94 is defined bymaking a hole passing through between the housing space 80 and anexterior space in the gear housing portion 62. An outside opening of thehole made is closed by a cap (not shown). The shaft feed flow passage 94is arranged to lead the oil O gathered in the first reservoir 93 intothe hollow portion 22 through the end portion of the shaft 21.

Referring to FIG. 1, the intra-shaft channel 91 c is a channel alongwhich the oil O passes in the hollow portion 22 of the shaft 21.Meanwhile, the intra-rotor channel 91 d is a channel along which the oilO passes from each communicating hole 23 of the shaft 21 through aninterior of the corresponding end plate 26, which is arranged on thecorresponding axial end surface 24 a of the rotor core 24, and isscattered to the stator 30 (see FIG. 5). That is, the first oil passage91 includes a channel arranged to pass from an interior of the shaft 21through the rotor core 24.

In the intra-shaft channel 91 c, a centrifugal force is applied to theoil O in the interior of the rotor 20 due to the rotation of the rotor20. Thus, the oil O is continuously scattered radially outward from eachend plate 26. In addition, the scattering of the oil O generates anegative pressure in the channel in the interior of the rotor 20,causing the oil O gathered in the first reservoir 93 to be sucked intothe interior of the rotor 20, so that the channel in the interior of therotor 20 is filled with the oil O. In addition, the travel of the oil Ointo the interior of the rotor 20 is facilitated by a capillary force inthe first oil passage 91. A portion of the oil O which has reached thestator 30 absorbs heat from the stator 30.

Referring to FIG. 1, the oil O is lifted from the oil pool P up to theupper side of the motor 2 and is fed to the motor 2 through the secondoil passage 92. The oil O fed to the motor 2 absorbs heat from thestator 30 while traveling on and along an outer circumferential surfaceof the stator 30, and thus cools the motor 2. After traveling on andalong the outer circumferential surface of the stator 30, the oil Odrips downward to be gathered in the lower region of the motor chamber81. The oil O passing through the second oil passage 92 joins the oil Opassing through the first oil passage 91 in the lower region of themotor chamber 81. The oil O gathered in the lower region of the motorchamber 81 travels to the lower region of the gear chamber 82 (i.e., tothe oil pool P) through the partition opening 68.

FIG. 10 is a sectional view of the motor assembly 1. Note that, in FIG.10, sections of several regions are shifted in the axial direction.

The second oil passage 92 includes a first flow passage 92 a, a secondflow passage 92 b, and a third flow passage 92 c. A pump 96, the cooler97, and the second reservoir 98 are arranged in a channel of the secondoil passage 92. In the second oil passage 92, the oil O passes throughthe first flow passage 92 a, the pump 96, the second flow passage 92 b,the cooler 97, the third flow passage 92 c, and the second reservoir 98in the order named, and is fed to the motor 2.

The pump 96 is an electric pump driven by electricity. The pump 96 isattached to a pump-attachment recessed portion 6 c arranged in the outersurface of the housing 6. The pump 96 includes a suction inlet 96 a anda discharge outlet 96 b. The suction inlet 96 a and the discharge outlet96 b are connected to each other through an internal flow passage of thepump 96. In addition, the suction inlet 96 a is connected to the firstflow passage 92 a. The discharge outlet 96 b is connected to the secondflow passage 92 b. The discharge outlet 96 b is arranged higher than thesuction inlet 96 a. The pump 96 is arranged to suck the oil O from theoil pool P through the first flow passage 92 a, and to feed the oil O tothe motor 2 through the second flow passage 92 b, the cooler 97, thethird flow passage 92 c, and the second reservoir 98.

The amount of a portion of the oil O which is fed to the motor 2 by thepump 96 is controlled appropriately in accordance with an operatingcondition of the motor 2. Accordingly, when the temperature of the motor2 has been increased, such as when a long-duration operation or a highpower output is required, the operation output of the pump 96 isincreased to increase the amount of the portion of the oil O which isfed to the motor 2.

The cooler 97 includes an inflow port 97 a and an outflow port 97 b. Theinflow port 97 a and the outflow port 97 b are connected to each otherthrough an internal flow passage of the cooler 97. In addition, theinflow port 97 a is connected to the second flow passage 92 b. Theoutflow port 97 b is connected to the third flow passage 92 c. Whencompared to the outflow port 97 b, the inflow port 97 a is arranged on aside closer to the pump 96 (i.e., on the lower side). In addition, acoolant pipe (not shown), in which a coolant supplied from a radiatorpasses, is arranged in an interior of the cooler 97. A portion of theoil O which passes in the interior of the cooler 97 is cooled throughheat exchange between the oil O and the coolant.

Each of the pump 96 and the cooler 97 is fixed to an outer peripheralsurface of the motor housing portion 61 of the housing 6. When viewed inthe axial direction of the motor axis J2, each of the pump 96 and thecooler 97 is arranged on an opposite side of the motor axis J2 withrespect to the differential 5 in a horizontal direction. In addition,the pump 96 and the cooler 97 are arranged one under the other in theup-down direction. The cooler 97 is arranged on the upper side of thepump 96. The cooler 97 is arranged to overlap with the pump 96 whenviewed in the vertical direction.

According to the present embodiment, an effective use of a spacesurrounding the motor 2 can be made by each of the pump 96 and thecooler 97 being arranged on the opposite side of the motor axis J2 withrespect to the differential 5. This makes it possible to reduce thedimension of the motor assembly 1 as a whole measured in the horizontaldirection, which leads to a reduced size of the motor assembly 1.

According to the present embodiment, each of the pump 96 and the cooler97 is fixed to an outer peripheral surface of the housing 6. This cancontribute to making the size of the motor assembly 1 smaller than inthe case where each of the pump 96 and the cooler 97 is placed externalto the housing 6. In addition, due to each of the pump 96 and the cooler97 being fixed to the outer peripheral surface of the housing 6, flowpassages that connect the housing space 80 to the pump 96 and the cooler97 can be defined by the first flow passage 92 a, the second flowpassage 92 b, and the third flow passage 92 c, each of which is arrangedto pass in an interior of a wall portion 6 a of the housing 6.

According to the present embodiment, the cooler 97 is fixed to the outerperipheral surface of the housing 6, and this leads to a reduceddistance between the housing space 80 and the cooler 97. Thus, the thirdflow passage 97 c, which connects the cooler 97 and the housing space 80to each other, can be made shorter to allow the cooled oil O to be fedto the housing space 80 while the temperature of the oil O is still low.

Each of the first flow passage 92 a, the second flow passage 92 b, andthe third flow passage 92 c is arranged to pass in the interior of thewall portion 6 a of the housing 6, which is arranged to surround thehousing space 80. Each of the first flow passage 92 a, the second flowpassage 92 b, and the third flow passage 92 c can be defined as a holedefined in the wall portion 6 a. This can contribute to reducing thenumber of parts, eliminating the need to prepare separate tubes.

The first flow passage 92 a is arranged to pass in an interior of aportion of the wall portion 6 a which lies on the lower side of themotor 2. The second flow passage 92 b is arranged to pass in an interiorof a portion of the wall portion 6 a which lies on a horizontal side ofthe motor 2. In addition, the third flow passage 92 c is arranged topass in an interior of a portion of the wall portion 6 a which lies onthe upper side of the motor 2.

The first flow passage 92 a is arranged to connect the oil pool P andthe pump 96 to each other. The first flow passage 92 a includes a firstend portion 92 aa and a second end portion 92 ab.

The first end portion 92 aa is arranged on an upstream side of thesecond end portion 92 ab along the second oil passage 92. The first endportion 92 aa is arranged to open into the housing space 80 on the lowerside of the differential 5. The first end portion 92 aa is arranged tooverlap with the motor 2 when viewed in the vertical direction.

The second end portion 92 ab is arranged to open into thepump-attachment recessed portion 6 c, and is connected to the suctioninlet 96 a of the pump 96.

As mentioned above, the differential 5 and the pump 96 are arranged onopposite horizontal sides of the motor axis J2. The first flow passage92 a is arranged to extend between the opposite horizontal sides thereofso as to extend across the motor 2. In addition, the first flow passage92 a is arranged to pass on the lower side of the motor 2.

According to the present embodiment, due to the first flow passage 92 apassing on the lower side of the motor 2, an effective use of a regionon the lower side of the motor 2 can be made to reduce the dimensions ofthe motor assembly 1. This leads to a reduced size of the motor assembly1.

At least a portion of the first flow passage 92 a is arranged to overlapwith each of the second gear 42 and the ring gear 51 when viewed in theaxial direction. This leads to a reduction in the dimensions of themotor assembly 1 when viewed in the axial direction, leading to areduced size of the motor assembly 1.

In the above description of the present embodiment, the case where eachof the second gear 42 and the ring gear 51, from among a plurality ofgears (i.e., the first gear 41, the second gear 42, the third gear 43,and the ring gear 51) that are connected between the motor 2 and thedifferential 5, overlaps with the first flow passage 92 a when viewed inthe axial direction has been described. Note, however, that theaforementioned effect can be achieved when at least one of the pluralityof gears that are connected between the motor 2 and the differential 5is arranged to overlap with the first flow passage 92 a when viewed inthe axial direction.

The first flow passage 92 a is arranged to extend from a position on thelower side of the differential 5 to the suction inlet 96 a of the pump96. The first flow passage 92 a is arranged to extend in a straight linewhile slanting upward as it extends from the first end portion 92 aa tothe second end portion 92 ab. In addition, the suction inlet 96 a of thepump 96 is arranged higher than a lower end of the differential 5 andlower than the motor axis J2.

In order to avoid a collision of a stone flying from a road surface withthe pump 96, it is preferable that the pump 96 is arranged at a positionaway from the road surface in a situation in which the motor assembly 1has been installed in the vehicle. Meanwhile, when the suction inlet 96a of the pump 96 is arranged to lie lower than an oil surface of the oilpool P, a reduction in the likelihood of sucking of air can be achieved.

The suction inlet 96 a according to the present embodiment is arrangedlower than the motor axis J2. This arrangement makes it easier toarrange the suction inlet 96 a to lie lower than the oil surface of theoil pool P. In addition, the suction inlet 96 a according to the presentembodiment is arranged higher than the lower end of the differential 5.This arrangement leads to the pump 96 being arranged away from the roadsurface. In addition, arranging the suction inlet 96 a lower than themotor axis J2 makes it easier to arrange the first flow passage 92 a toextend in a straight line. This leads to an increase in the ease withwhich the first flow passage 92 a is defined in the case where the firstflow passage 92 a is arranged to pass in the interior of the wallportion 6 a of the housing 6.

The suction inlet 96 a according to the present embodiment is arrangedto lie lower than the liquid surface of the oil pool P in the housingspace 80. Notice that the level of the liquid surface of the oil pool Pvaries in accordance with feeding of the oil O from the oil pool P toeach of the first oil passage 91 and the second oil passage 92. Thesuction inlet 96 a is arranged to lie lower than the liquid surface ofthe oil pool P even when the liquid surface of the oil pool P is at thelowest level.

In FIG. 1, the suction inlet 96 a is depicted as lying higher than theliquid surface of the oil pool P. However, FIG. 1 is merely a schematicdiagram, and it is to be understood that the actual suction inlet 96 alies lower than the liquid surface of the oil pool P.

The second flow passage 92 b is arranged to connect the pump 96 and thecooler 97 to each other. The second flow passage 92 b includes a firstend portion 92 ba and a second end portion 92 bb. The first end portion92 ba is arranged to open into the pump-attachment recessed portion 6 c,and is connected to the discharge outlet 96 b of the pump 96. The firstend portion 92 ba is arranged on the upstream side of the second endportion 92 bb along the second oil passage 92. The second end portion 92bb is connected to the inflow port 97 a of the cooler 97. The second endportion 92 bb is arranged higher than the first end portion 92 ba.

The second flow passage 92 b includes a first passage 92 bd and a secondpassage 92 be. The first passage 92 bd is arranged to extend upward fromthe pump-attachment recessed portion 6 c. The second passage 92 be isarranged to extend in a horizontal direction from an upper end of thefirst passage 92 bd. The first passage 92 bd and the second passage 92be are defined by making holes extending from different directions tointersect each other in the wall portion 6 a of the housing 6.

The third flow passage 92 c is arranged to connect the cooler 97 and thehousing space 80 to each other. The third flow passage 92 c is arrangedto extend in a straight line along a horizontal direction. The thirdflow passage 92 c includes a first end portion 92 ca and a second endportion 92 cb. The first end portion 92 ca is arranged on the upstreamside of the second end portion 92 cb along the second oil passage 92.The first end portion 92 ca is connected to the outflow port 97 b of thecooler 97. The second end portion 92 cb is arranged to open into thehousing space 80 on the upper side of the motor 2. That is, the thirdflow passage 92 c is arranged to open into the housing space 80 on theupper side of the motor 2. The second end portion 92 cb of the thirdflow passage 92 c functions as a feed portion 99 arranged to feed theoil O to the second reservoir 98, which is arranged in the housing space80. That is, the second oil passage 92 is arranged to feed the oil O tothe second reservoir 98 at the feed portion 99.

The outflow port 97 b of the cooler 97 is arranged to overlap with themotor 2 in the axial direction of the motor axis J2. That is, theoutflow port 97 b of the cooler 97 is arranged to overlap with the motor2 when viewed in a radial direction. In other words, the outflow port 97b of the cooler 97 is arranged between both end portions of the stator30 in the axial direction. Thus, the third flow passage 92 c, whichconnects the outflow port 97 b of the cooler 97 and the housing space 80to each other, can be made shorter to allow the cooled oil O to be fedto the housing space 80 while the temperature of the oil O is still low.In addition, the third flow passage 97 c and the motor 2 are arranged tooverlap with each other when viewed in a radial direction, and thisleads to a reduced axial dimension of the motor assembly 1, which leadsto a reduced size of the motor assembly 1.

FIG. 11 is a perspective view of the motor assembly 1. FIG. 12 is a planof the second reservoir 98. Note that, in FIG. 11, the motor housingportion 61 and the closing portion 63 of the housing 6 are not shown.

Referring to FIG. 11, the second reservoir (i.e., a main reservoir) 98is arranged in the motor chamber 81 of the housing space 80. The secondreservoir 98 is arranged on the upper side of the motor 2. The secondreservoir 98 includes bottom portions (i.e., a first bottom portion 98 cand a second bottom portion 98 g) and side wall portions (i.e., a firstside wall portion 98 d, a second side wall portion 98 e, a third sidewall portion 98 f, a fourth side wall portion 98 h, a fifth side wallportion 98 i, a sixth side wall portion 98 j, and a seventh side wallportion 98 n) arranged to extend upward from the bottom portions. Thesecond reservoir 98 is arranged to store a portion of the oil O whichhas been fed into the motor chamber 81 through the feed portion 99 ofthe third flow passage 92 c in a space surrounded by the bottom portionsand the side wall portions. The second reservoir 98 includes a pluralityof outflow ports (i.e., a first outflow port 98 r, a second outflow port98 o, a third outflow port 98 x, a fourth outflow port 98 t, a fifthoutflow port 98 u, and a sixth outflow port 98 v). Each outflow port isarranged to feed a portion of the oil O gathered in the second reservoir98 to the motor 2. That is, the second reservoir 98 is arranged to feedthe oil O stored therein to various portions of the motor 2 from theupper side through the outflow ports.

According to the present embodiment, the second reservoir 98 is arrangedon the upper side of the motor 2 to feed the oil O stored therein to theupper side of the motor 2 through the plurality of outflow ports. Theoil O flows downward on and along an outer peripheral surface of themotor 2 while absorbing heat from the motor 2, and is thus able to coolthe whole motor 2.

Referring to FIG. 12, the second reservoir 98 includes a first endportion 98 p arranged on a side closer to the gear chamber 82 in theaxial direction, and a second end portion 98 q arranged on a sideopposite to the first end portion 98 p in the axial direction. Inaddition, the second reservoir 98 includes a gutter-like first storageportion 98A arranged to extend along the axial direction, and a secondstorage portion 98B arranged on a side of the first storage portion 98Acloser to the second end portion 98 q.

The first storage portion 98A has the first bottom portion 98 c, thefirst side wall portion 98 d, the second side wall portion 98 e, and thethird side wall portion 98 f. In addition, the first outflow port 98 r,the second outflow port 98 o, and the third outflow port 98 x arearranged in the first storage portion 98A.

The first bottom portion 98 c is rectangular with a longitudinaldirection thereof being parallel to the axial direction. Both axial endportions of the first bottom portion 98 c are arranged on the upper sideof the coil ends 31 a, which are arranged at both end portions of thestator 30. The first outflow port 98 r is defined in the first bottomportion 98 c. The first outflow port 98 r is arranged in a region of thefirst bottom portion 98 c close to the first end portion 98 p.

Each of the first side wall portion 98 d and the second side wallportion 98 e is arranged to extend along the axial direction. Inaddition, the first and second side wall portions 98 d and 98 e arearranged opposite to each other in the circumferential direction aboutthe motor axis J2.

An inflow port 98 s is defined in the first side wall portion 98 d. Theinflow port 98 s is a cut in the shape of the letter “U” and openingupward. The feed portion 99 is connected to the inflow port 98 s. Theinflow port 98 s is arranged near the axial middle of the first sidewall portion 98 d. This arrangement enables the inflow port 98 s to passthe oil O toward both the first end portion 98 p and the second endportion 98 q in the second reservoir 98.

The second side wall portion 98 e includes a protruding portion 98 warranged to protrude toward the first side wall portion 98 d. Theprotruding portion 98 w is arranged directly opposite to the inflow port98 s. The protruding portion 98 w includes a slanting surface arrangedto decrease the extent to which the protruding portion 98 w protrudes asit extends from the middle toward each of the first end portion 98 p andthe second end portion 98 q. The protruding portion 98 w smoothlydivides a portion of the oil O which has flowed into the secondreservoir 98 through the inflow port 98 s into two portions, one flowingtoward the first end portion 98 p and the other flowing toward thesecond end portion 98 q.

The second outflow port 98 o is defined in the second side wall portion98 e. The second outflow port 98 o is arranged in a region of the secondside wall portion 98 e close to the first end portion 98 p. The secondoutflow port 98 o is arranged in the vicinity of the first outflow port98 r.

Referring to FIG. 11, the third side wall portion 98 f is arranged onthe side of the second reservoir 98 on which the first end portion 98 plies. The third side wall portion 98 f is arranged on the upper side ofthe coil ends 31 a on one side of the stator 30. An upper end portion ofthe third side wall portion 98 f is arranged at a level lower than thatof an upper end portion of the first side wall portion 98 d and that ofan upper end portion of the second side wall portion 98 e. In addition,the level of the upper end portion of the third side wall portion 98 fis substantially equal to the level of a lower end of an opening of thesecond outflow port 980. A space on the upper side of the third sidewall portion 98 f functions as the third outflow port 98 x, which allowsa portion of the oil O to flow out therethrough when the liquid level ofthe oil O gathered in the second reservoir 98 has become high.

The second storage portion 98B is arranged to extend in acircumferential direction of the stator 30. The second storage portion98B has the second bottom portion 98 g, the fourth side wall portion 98h, the fifth side wall portion 98 i, the sixth side wall portion 98 j,the seventh side wall portion 98 n, and a shoulder portion 98 k.

In addition, the fourth outflow port 98 t, the fifth outflow port 98 u,the sixth outflow port 98 v, and an overflow portion 98 y are arrangedin the second storage portion 98B.

The second bottom portion 98 g is arranged on the side of the firstbottom portion 98 c on which the second end portion 98 q lies. Thesecond bottom portion 98 g is arranged lower than the first bottomportion 98 c. The shoulder portion 98 k is defined at a boundary betweenthe first bottom portion 98 c and the second bottom portion 98 g. Thesecond storage portion 98B is arranged lower than the first storageportion 98A. A portion of the oil O which has flowed toward the secondend portion 98 q in the first storage portion 98A is gathered in thesecond storage portion 98B.

The second bottom portion 98 g is arranged on the upper side of the coilends 31 a on one side of the stator 30. The second bottom portion 98 gis arranged to curve along the outer peripheral surface of the motor 2.This arrangement contributes to increasing the volume of oil O that canbe stored in the second reservoir 98 without increasing the dimensionsof the motor assembly 1. The second bottom portion 98 g is arranged toslant downward as it extends from a position that overlaps with themotor axis J2 when viewed in the up-down direction to either side in thecircumferential direction. The second storage portion 98B is connectedto the first storage portion 98A on one side of the motor axis J2 whenviewed in the up-down direction.

Referring to FIG. 12, the second storage portion 98B is divided into afirst region 98 gA, which is a region connected to the first storageportion 98A on one side of the motor axis J2 when viewed in the up-downdirection, and a second region 98 gB, which is a region on another sideof the motor axis J2. The second bottom portion 98 g is arranged to behighest at a boundary line between the first region 98 gA and the secondregion 98 gB. A portion of the oil O which has flowed from the firststorage portion 98A into the second storage portion 98B is firstgathered in the first region 98 gA, and at a time when the liquid levelin the first region 98 gA has reached the level of the boundary line, aportion of the oil O flows into the second region 98 gB. Thus, theboundary line functions as a barrier 98 gC arranged in the second bottomportion 98 g. That is, the second bottom portion 98 g includes thebarrier 98 gC, which is arranged to project upward to divide the secondstorage portion 98B of the second reservoir 98 into the first region 98gA and the second region 98 gB. After the oil O flows into one of theregions (i.e., the first region 98 gA) and the liquid level thereinrises above the barrier 98 gC, the oil O flows into the other region(i.e., the second region 98 gB).

As will be described below, the fourth outflow port 98 t, the fifthoutflow port 98 u, and the sixth outflow port 98 v, which are arrangedalong the circumferential direction, are defined in the sixth side wallportion 98 j, which is arranged to extend along the circumferentialdirection. In addition, the overflow portion 98 y is defined in thefifth side wall portion 98 i. Each of the fourth outflow port 98 t andthe fifth outflow port 98 u is arranged to open into the first region 98gA, while each of the sixth outflow port 98 v and the overflow portion98 y is arranged to open into the second region 98 gB. That is, in thesecond reservoir 98, at least one outflow port is arranged at each of aplurality of regions (i.e., the first region 98 gA and the second region98 gB) divided by the barrier 98 gC. Thus, before the liquid level inthe first region 98 gA rises above the barrier 98 gC, the oil O flowsout through only the fourth outflow port 98 t and the fifth outflow port98 u. After the liquid level in the first region 98 gA has risen abovethe barrier 98 gC, the oil O flows out through the fourth outflow port98 t, the fifth outflow port 98 u, the sixth outflow port 98 v, and theoverflow portion 98 y. Thus, the second reservoir 98 according to thepresent embodiment is arranged to increase the number of outflow portsthrough which the oil O flows out when the amount of the oil O stored inthe second reservoir 98 has become large. In particular, when a load onthe motor 2 has become high and the temperature of the motor 2 hasbecome high, the amount of a portion of the oil O which is fed to thesecond reservoir 98 by the pump 96 becomes large. Accordingly, accordingto the present embodiment, when the temperature of the motor 2 hasbecome high, the number of points through which the oil O is fed to themotor 2 can be increased to enlarge a cooling area, and the amount ofthe portion of the oil O which is fed to the motor 2 can be increased.

The fourth side wall portion 98 h and the fifth side wall portion 98 iare arranged at both circumferential end portions of the second storageportion 98B. The fourth side wall portion 98 h and the fifth side wallportion 98 i are arranged opposite to each other in the circumferentialdirection. Each of the fourth side wall portion 98 h and the fifth sidewall portion 98 i is arranged to extend along the axial direction. Thefourth side wall portion 98 h is arranged to extend toward the secondend portion 98 q continuously from the first side wall portion 98 d.

The overflow portion 98 y is defined in the fifth side wall portion 98i. The overflow portion 98 y is a portion at an upper end of the fifthside wall portion 98 i which has a locally reduced height. The overflowportion 98 y is arranged higher than each of lower ends of openings ofthe fourth outflow port 98 t, the fifth outflow port 98 u, and the sixthoutflow port 98 v of the second storage portion 98B. Therefore, the oilO overflows through the overflow portion 98 y after the liquid level inthe second storage portion 98B has become higher than the fourth outflowport 98 t, the fifth outflow port 98 u, and the sixth outflow port 98 v.The auxiliary reservoir 95, which will be described below, is arrangedon the lower side of the overflow portion 98 y. A portion of the oil Owhich overflows through the overflow portion 98 y is stored in theauxiliary reservoir 95.

Note that the term “to overflow” as used in the present specificationrefers to flowing out of a reservoir when a liquid in the reservoir hasreached a certain liquid level. Therefore, when a liquid flows outthrough a bottom portion of a reservoir or the like, the liquid is notdescribed as “overflowing”.

The sixth side wall portion 98 j is arranged on the side of the secondreservoir 98 on which the second end portion 98 q lies. The sixth sidewall portion 96 j is arranged to extend along the circumferentialdirection. The sixth side wall portion 98 j is arranged on the upperside of the coil ends 31 a on one side of the stator 30. Each of thefourth outflow port 98 t, the fifth outflow port 98 u, and the sixthoutflow port 98 v is defined in the sixth side wall portion 98 j. Eachof the fourth outflow port 98 t, the fifth outflow port 98 u, and thesixth outflow port 98 v is a hole defined in the sixth side wall portion98 j and passing through from an interior of the second reservoir 98 toan exterior space. The fourth outflow port 98 t, the fifth outflow port98 u, and the sixth outflow port 98 v are arranged along thecircumferential direction. Referring to FIG. 11, each of the fourthoutflow port 98 t, the fifth outflow port 98 u, and the sixth outflowport 98 v is arranged at a different level. Accordingly, according tothe present embodiment, the number of outflow ports through which theoil O flows out can be increased in accordance with the liquid level ofthe oil O in the second reservoir 98. The number of points through whichthe oil O is fed to the motor 2 can thus be increased to enlarge thecooling area, and the amount of the portion of the oil O which is fed tothe motor 2 can thus be increased.

Note that the above effects can be achieved when at least two of aplurality of outflow ports defined in the second reservoir 98 arearranged at mutually different levels.

The seventh side wall portion 98 n is arranged to extend along thecircumferential direction. The seventh side wall portion 98 n isarranged opposite to the sixth side wall portion 98 j in the axialdirection. The seventh side wall portion 98 n is arranged to becontinuous with the shoulder portion 98 k along the circumferentialdirection. A housing portion 98 na, in which a fixing screw for thestator core 32 is housed, is arranged at the seventh side wall portion97 n.

According to the present embodiment, the second oil passage 92 isarranged to feed the oil O stored in the second reservoir 98 to themotor 2 through a plurality of outflow ports. Each of the outflow portsis arranged to feed the oil O to the motor 2 at a constant flow rate,and this arrangement leads to an increase in efficiency with which themotor 2 is cooled by the oil O.

According to the present embodiment, the second reservoir 98 includes aplurality of outflow ports (i.e., the first outflow port 98 r, thesecond outflow port 98 o, the third outflow port 98 x, the fourthoutflow port 98 t, the fifth outflow port 98 u, and the sixth outflowport 98 v). Accordingly, the second reservoir 98 is able to feed the oilO to the motor 2 through a plurality of positions at the same time, andis able to cool various portions of the motor 2 at the same time.

According to the present embodiment, the second reservoir 98 is arrangedto extend along the axial direction. In addition, at least one of theoutflow ports is arranged at each of both axial end portions of thesecond reservoir 98. Further, the outflow ports arranged at both axialend portions of the second reservoir 98 are arranged on the upper sideof the coil ends 31 a. This allows the oil O to be poured on the coilends 31 a arranged at both axial ends of the stator 30 to directly coolthe coils 31. More specifically, the oil O poured on the coils 31penetrates the coils 31 through gaps between conducting wires of thecoils 31. Portions of the oil O which have penetrated the coils 31absorb heat from the coils 31 while permeating throughout the coils 31due to gravity and capillary forces acting between the conducting wires.Further, the oil O is gathered at a lowermost portion of an innercircumferential surface of the stator core 32, and drips through bothaxial ends of the coils 31.

Note that the effect of directly cooling the coils 31 by directlyfeeding the oil O to the coil ends 31 a can be achieved when at leasttwo of the plurality of outflow ports are arranged at both axial endportions of the second reservoir 98.

According to the present embodiment, the feed portion 99, which isarranged to feed the oil O to the second reservoir 98, is arrangedbetween the outflow ports arranged at both end portions of the secondreservoir 98 in the axial direction. This arrangement enables the oil Ofed through the feed portion 99 to flow out through the outflow portsarranged at both the end portions.

FIG. 13 is a perspective view of a second reservoir 198 according to amodification, which can be adopted in the present embodiment. Note that,in the following description, elements that have their equivalents inthe above-described embodiment are denoted by the same referencecharacters as those of their equivalents in the above-describedembodiment.

The second reservoir 198 according to this modification is in the shapeof a shallow rectangular box that opens upward. The second reservoir 198includes a central oil storage portion 198 a and four oil feed portions198 b arranged around the central oil storage portion 198 a. The centraloil storage portion 198 a and the four oil feed portions 198 b areseparated from one another.

The central oil storage portion 198 a is arranged to gather a portion ofthe oil O which flows in from the feed portion 99. The central oilstorage portion 198 a is separated from the oil feed portions 198 b by acircular bottom surface 198 ab and a cylindrical wall 198 aa arranged toextend upward from the bottom surface 198 ab.

The four oil feed portions 198 b are arranged to surround the centraloil storage portion 198 a. Each oil feed portion 198 b is arranged tohave a substantially rectangular shape. Each oil feed portion 198 bincludes outflow ports 198 c, each of which is arranged to bring aninterior of the oil feed portion 198 b into communication with anexterior space, and each of which is arranged in the vicinity of acorner portion between two outer walls 198 ba of the oil feed portion198 b arranged to extend in mutually different directions. One of thetwo outflow ports 198 c is arranged to open in the axial direction ofthe motor 2, while another one of the two outflow ports 198 c isarranged to open in the circumferential direction. Since each of thefour oil feed portions 198 b includes two of the outflow ports 198 c,the second reservoir 198 includes a total of eight outflow ports 198 c.

The second reservoir 198 is placed on the upper side of the stator 30such that a bottom surface thereof is oriented horizontally. Afterfilling the central oil storage portion 198 a, the oil O fed from thefeed portion 99 overflows across the cylindrical wall 198 aa to flowinto the four oil feed portions 198 b. Since the second reservoir 198 isplaced horizontally, and because the cylindrical wall 198 aa is arrangedto have a uniform height over 360 degrees, the oil O flows equally intothe four oil feed portions 198 b. The oil O is gathered in each of thefour oil feed portions 198 b, and flows out to the exterior spacethrough each outflow port 198 c.

The dimension of the second reservoir 198 along the axial direction isarranged to be greater than the dimension of the stator core 32 alongthe axial direction. The oil O is fed from each oil feed portion 198 bto the motor 2 through the two outflow ports 198 c, which face in theaxial direction and the circumferential direction, respectively.According to the present modification, the second reservoir 198 is ableto feed the oil O in a plurality of directions from a plurality ofoutflow ports to the motor 2.

FIG. 14 is a sectional view of the motor assembly 1, illustrating anoutline of the auxiliary reservoir 95. Note that, in FIG. 14, theprojecting portion 63 d arranged in the closing portion 63 of thehousing 6 is represented by an imaginary line. Also note that, in FIG.14, the oil O stored in the auxiliary reservoir 95 is emphasized by adot pattern.

The auxiliary reservoir 95 is arranged to receive a portion of the oil Owhich has overflowed from the second reservoir 98 in the second oilpassage 92. That is, the auxiliary reservoir 95, which is arranged tostore the oil O, is arranged in the channel of the second oil passage92. The second reservoir 98 functions as the main reservoir for theauxiliary reservoir 95. The second reservoir 98 is arranged on theupstream side of the auxiliary reservoir 95 in the second oil passage92.

The auxiliary reservoir 95 is arranged directly below the overflowportion 98 y. That is, the auxiliary reservoir 95 and the overflowportion 98 y are arranged to overlap with each other when viewed in thevertical direction. Thus, the portion of the oil O which has overflowedfrom the second reservoir 98 can be received by the auxiliary reservoir95.

The auxiliary reservoir 95 includes a first portion 95A arranged on onecircumferential side of the second reservoir 98, and a second portion95B arranged on another circumferential side of the second reservoir 98.The first portion 95A and the second portion 95B are connected to eachother. The auxiliary reservoir 95 includes a total of four outflow ports61 k, two of which are arranged in each of the first portion 95A and thesecond portion 95B. The four outflow ports 61 k are arranged along thecircumferential direction of the motor 2. In addition, the outflow ports61 k are arranged at mutually different levels.

The auxiliary reservoir 95 is defined by an inside surface 61 g of themotor housing portion 61 and an inner wall surface of the projectingportion 63 d of the closing portion 63. The inside surface 61 g of themotor housing portion 61 includes an inner peripheral surface 61 iarranged to face radially inward, and an opposed surface 61 h arrangedto face toward the closing portion 63 in the axial direction. Theopposed surface 61 h is arranged to be in contact with a surface of theprojecting portion 63 d which faces in the axial direction. The oil Odoes not flow out through a junction between the projecting portion 63 dand the opposed surface 61 h. According to the present embodiment, theauxiliary reservoir 95 is defined as a gap between other members, andthis eliminates the need to use another member, and contributes topreventing an increase in the number of parts.

The opposed surface 61 h includes recessed portions 61 j arranged alongthe circumferential direction, each recessed portion 61 j being recessedin the axial direction. Each recessed portion 61 j is recessed in such adirection as to enlarge a gap between the inside surface 61 g of themotor housing portion 61 and the inner wall surface of the projectingportion 63 d. The oil O flows out downward through each recessed portion61 j. That is, each recessed portion 61 j defines one of the outflowports 61 k. Each outflow port 61 k is arranged on the upper side of thecoil ends 31 a of the stator 30. Accordingly, a portion of the oil Owhich flows out through each outflow port 61 k cools the coils 31 of thecoil ends 31 a.

In the present embodiment, the description of which is provided by wayof example, at a junction between the inside surface 61 g of the motorhousing portion 61 and the inner wall surface of the projecting portion63 d, each recessed portion 61 j is defined in the inside surface 61 g.Note, however, that each recessed portion may alternatively be definedin the inner wall surface of the projecting portion 63 d.

According to the present embodiment, provision of the auxiliaryreservoir 95 in addition to the second reservoir 98 enables the oil O toflow out through the outflow ports 61 k of the auxiliary reservoir 95 inaddition to the outflow ports of the second reservoir 98, enablingcooling of a larger area of the motor 2. In addition, the outflow ports61 k of the auxiliary reservoir 95 are arranged along thecircumferential direction. This arrangement enables the coil ends 31 aof the stator 30 to be cooled over a large area. Further, since theoutflow ports 61 k are arranged at mutually different levels, the oil Ocan be caused to flow out therethrough at different times in accordancewith the liquid level of the oil O gathered in the auxiliary reservoir95.

According to the present embodiment, the portion of the oil O which hasoverflowed from the second reservoir 98 is stored in the auxiliaryreservoir 95. The pump 96 increases the amount of the portion of the oilO which is fed to the second reservoir 98 when the load on the motor 2has become high and the temperature of the motor 2 has become high.Therefore, when the load on the motor 2 has become high, the oil Ooverflows from the second reservoir 98, enabling the oil O to be fed tothe motor 2 through the outflow ports 61 k of the auxiliary reservoir 95as well. According to the present embodiment, when the load on the motor2 has become high, the motor 2 can be cooled by the oil O over a largearea. That is, the provision of the auxiliary reservoir 95 makes itpossible to automatically enlarge the area over which the oil O is fedto the motor 2 when an operation of the motor 2 has shifted from asteady state to a high-load state.

In addition, a lower end of the auxiliary reservoir 95 according to thepresent embodiment is arranged higher than the motor axis J2.Accordingly, each outflow port 61 k of the auxiliary reservoir 95 isarranged higher than the motor axis J2. The motor 2 is substantiallycolumnar. Arranging the lower end of the auxiliary reservoir 95 higherthan the motor axis J2 enables a portion of the oil O which has flowedout through each outflow port 61 k to travel on and along a surface ofthe motor 2 to cool the motor 2. In addition, the motor 2 is widest in ahorizontal section passing through the motor axis J2. Since the lowerend of the auxiliary reservoir 95 is arranged higher than the motor axisJ2, the oil O traveling on and along the surface of the motor 2 passes aregion where the motor 2 has the greatest horizontal width. This leadsto efficient cooling of the motor 2.

Referring to FIG. 1, when the motor 2 is in operation, the oil O is fedto the motor 2 through the first oil passage 91 and the second oilpassage 92. After being fed to the motor 2, the oil O drips downwardwhile cooling the motor 2, and is gathered in the lower region of themotor chamber 81. After being gathered in the lower region of the motorchamber 81, the oil O travels into the gear chamber 82 through thepartition opening 68 defined in the partition 61 c.

FIG. 15 is a front view of the partition 61 c of the housing 6 as viewedfrom the motor chamber 81.

The partition opening 68 is arranged lower than the insert hole 61 f,through which the shaft 21 is inserted. The partition opening 68includes a first opening portion 68 a and a second opening portion 68 barranged higher than the first opening portion 68 a. Each of the firstopening portion 68 a and the second opening portion 68 b is arranged tobring the motor chamber 81 and the gear chamber 82 into communicationwith each other.

Referring to FIG. 19, a lower end of the partition opening 68 (i.e., alower end of the first opening portion 68 a) is arranged higher than aminimum level Lmin of the liquid surface of the oil O in the gearchamber 82 when the motor 2 is at rest. This arrangement allows thepartition opening 68 to transfer as much of the oil O as possible intothe oil pool P when the motor 2 is in a stopped state, in which themotor 2 is at rest.

Referring to FIG. 15, the first opening portion 68 a is circular in planview. The lower end of the first opening portion 68 a is arranged lowerthan a lower end of the stator 30. The first opening portion 68 a isarranged in the vicinity of the bottom portion 81 a of the motor chamber81. Accordingly, the first opening portion 68 a allows the oil O to betransferred to the gear chamber 82 therethrough until the oil O gatheredin the lower region of the motor chamber 81 almost runs out.

The first opening portion 68 a is arranged to overlap with the motoraxis J2 when viewed in the up-down direction. In addition, the firstopening portion 68 a is arranged at a recessed portion 61 q defined inthe inner peripheral surface of the peripheral wall portion 61 a. Here,the peripheral wall portion 61 a and the recessed portion 61 q will nowbe described below. The motor housing portion 61 of the housing 6includes the peripheral wall portion 61 a, which is arranged to have acylindrical shape, extending along the outer circumferential surface ofthe stator 30. The recessed portion 61 q, which is recessed radiallyoutward, is defined in the inner peripheral surface of the peripheralwall portion 61 a. The recessed portion 61 q is arranged to extend alongthe axial direction. The recessed portion 61 q is arranged directlybelow the motor axis J2. That is, the recessed portion 61 q is arrangedto overlap with the motor axis J2 when viewed in the up-down direction.Due to the cylindrical shape of the peripheral wall portion 61 a, theoil O in the motor chamber 81 travels on and along the inner peripheralsurface of the peripheral wall portion 61 a to collect in an interior ofthe recessed portion 61 q. The first opening portion 68 a, beingarranged at the recessed portion 61 q, allows a portion of the oil O inthe motor chamber 81 which has been collected in the interior of therecessed portion 61 q to be efficiently transferred to the gear chamber82.

The second opening portion 68 b is arranged higher than the firstopening portion 68 a. The second opening portion 68 b is rectangularwith a longitudinal direction thereof being parallel to a horizontaldirection in plan view. The second opening portion 68 b is arranged tohave an opening area greater than that of the first opening portion 68a. In addition, the second opening portion 68 b is arranged to have agreater width along the horizontal direction than the first openingportion 68 a. The second opening portion 68 b includes a lower end 68 carranged to extend along the horizontal direction.

Driving of the motor 2 increases the amount of a portion of the oil Owhich is fed to the motor 2 through the oil passage 90 (i.e., the firstoil passage 91 and the second oil passage 92) per unit time. As aresult, the liquid level of the oil O gathered in the lower region ofthe motor chamber 81 rises. In the partition opening 68, a region whichlies lower than the liquid surface of the oil O gathered in the lowerregion of the motor chamber 81, and a region which lies higher than theliquid surface, are referred to as a first region S and a second regionR, respectively. The partition opening 68 is arranged to allow the oil Oto be transferred to the gear chamber 82 through the first region S. Arise in the liquid surface of the oil O gathered in the lower region ofthe motor chamber 81 will cause an increase in the area of the firstregion S and a reduction in the area of the second region R. Theincrease in the area of the first region S leads to an increase in theamount of transfer of the oil O from the motor chamber 81 to the gearchamber 82 through the partition opening 68.

The partition opening 68 according to the present embodiment is arrangedsuch that a rise in the liquid surface of the oil O in the motor chamber81 will cause an increase in the amount of transfer of the oil O fromthe motor chamber 81 to the gear chamber 82 through the partitionopening 68. This arrangement contributes to preventing an excessive risein the liquid level of the oil O in the motor chamber 81. That is, areduction in the likelihood that the rotor 20 in the motor chamber 81will soak in the oil O or excessively scrape up the oil O can beachieved. Accordingly, a reduction in the likelihood that rotationefficiency of the motor 2 will be reduced by flow resistance of the oilO can be achieved.

In addition, according to the present embodiment, an effective use ofthe oil O in the motor assembly 1 can be made by causing the oil O inthe motor chamber 81 to be transferred to the gear chamber 82 inaccordance with the level of the liquid surface of the oil O in themotor chamber 81. Thus, the amount of the oil O used can be reduced,resulting not only in a reduction in the weight of the motor assembly 1,but also in an increase in efficiency of energy use required to cool theoil O.

Referring to FIG. 19, the lower end of the second opening portion 68 bis arranged to lie higher than the level (i.e., a maximum level Lmax orthe minimum level Lmin) of the liquid surface of the oil O in the gearchamber 82 regardless of whether the motor 2 is at rest or in operation.This arrangement prevents the second opening portion 68 b from beingburied in the oil O in the gear chamber 82. The second opening portion68 b allows the oil O to be transferred to the gear chamber 82therethrough regardless of the liquid level in the gear chamber 82 toprevent the rotor 20 from soaking in the oil O.

A variation in the amount of transfer of the oil O through the partitionopening 68 which accompanies a rise in the liquid surface of the oil Ogathered in the lower region of the motor chamber 81 will now bedescribed more specifically below. Here, a liquid level reaching thelower end 68 c of the second opening portion 68 b and being a liquidlevel of the oil O gathered in the lower region of the motor chamber 81is defined as a first liquid level OL. That is, the lower end of thesecond opening portion 68 b is arranged at the first liquid level OL.The first liquid level OL lies higher than the lower end of the stator30 and lower than a lower end of the rotor 20.

FIG. 16 is a graph showing the relationship between the level of theliquid level of the oil O gathered in the lower region of the motorchamber 81 and the area of the first region S. The area of the firstregion S is correlated to (substantially proportional to) the flow rateat which the oil O flows out through the partition opening 68.

Once the motor 2 is driven, the oil O is fed to the motor 2, and startsto be gathered in the lower region of the motor chamber 81. The oil Ogathered in the lower region of the motor chamber 81 travels from themotor chamber 81 into the gear chamber 82 through the first openingportion 68 a. When the amount of the portion of the oil O which is fedto the motor 2 per unit time has exceeded the flow rate at which the oilO is transferred from the motor chamber 81 to the gear chamber 82through the first opening portion 68 a, the liquid level of the oil Ogathered in the lower region of the motor chamber 81 rises. Once theliquid level reaches the first liquid level OL, the oil O flows outthrough the second opening portion 68 b in addition to the first openingportion 68 a. Since the second opening portion 68 b has a greater widthalong the horizontal direction than the first opening portion 68 a, thearea of the first region S rapidly increases when the liquid levelreaches the first liquid level OL. Accordingly, the flow rate at whichthe oil O flows from the motor chamber 81 into the gear chamber 82through the partition opening 68 rapidly increases. As mentioned above,the first liquid level OL is set lower than the lower end of the rotor20. Accordingly, according to the present embodiment, a reduction in thelikelihood that rotation efficiency of the rotor 20 in the motor chamber81 will be reduced by the flow resistance of the oil O can be achieved.

The second opening portion 68 b is preferably arranged to have such awidth along the horizontal direction as to make the flow rate at whichthe oil O flows out through the partition opening 68 when the liquidlevel has become higher than the first liquid level OL higher than theflow rate at which the oil O is fed to the motor 2 through the oilpassage 90. This arrangement will contribute to preventing the liquidlevel of the oil O gathered in the lower region of the motor chamber 81from considerably exceeding the first liquid level OL, and to preventingthe rotor 20 from soaking in the oil O.

Referring to FIG. 1, the first oil passage 91 includes the scraping-upchannel 91 a and the intra-rotor channel 91 d. The scraping-up channel91 a transfers the oil O from the gear chamber 82 to the motor chamber81 through the scraping up of the oil O by the differential 5. Theamount of the portion of the oil O which is scraped up by thedifferential 5 depends on the rotation rate of the differential 5.Accordingly, the amount of transfer of the oil O to the motor chamber 81through the scraping-up channel 91 a varies depending on the vehiclespeed. Meanwhile, the intra-rotor channel 91 d sucks the oil O throughthe centrifugal force of the rotor 20 so that the oil O will travel awayfrom the gear chamber 82 toward the motor chamber 81. The centrifugalforce depends on the rotation rate of the rotor 20. Accordingly, theamount of transfer of the oil O to the motor chamber 81 through theintra-rotor channel 91 d varies depending on the vehicle speed. That is,the amount of transfer of the oil O to the motor chamber 81 through thefirst oil passage 91 varies depending on the vehicle speed.

Meanwhile, the second oil passage 92 transfers the oil O from the gearchamber 82 to the motor chamber 81 through the pump (i.e., the electricpump) 96. The amount of the portion of the oil O which is fed throughthe pump 96 is controlled on the basis of, for example, a measuredtemperature of the motor 2. Accordingly, the amount of transfer of theoil O to the motor chamber 81 through the second oil passage 92 variesregardless of the vehicle speed.

The second oil passage 92 stops the feeding of the oil 0 to the motor 2when the motor 2 is at rest. In addition, the second oil passage 92starts the transfer of the oil O to the motor chamber 81 when the motor2 is started. Therefore, the level of the liquid surface of the oil poolP in the gear chamber 82 can be raised when the motor 2 is at rest. Thisenables the rotation of the motor 2 immediately after the start thereofto cause each of the second gear 42, the third gear 43, and the ringgear 51 to rotate in the oil pool P to cause the oil O to spreadthroughout the tooth faces thereof.

According to the present embodiment, the second oil passage 92 lifts theoil O from the oil pool P independently of the speed of the vehicle.Accordingly, the second oil passage 92 can lower the level of the oilsurface of the oil pool P even when the vehicle is traveling at a lowspeed. Thus, the likelihood that rotation efficiency of the gears in thegear chamber 82 will be reduced by the oil O in the oil pool P when thevehicle is traveling at a low speed can be reduced.

FIG. 17 is a front view of a partition opening 168 according to amodification, which can be adopted in the present embodiment. Note that,in the following description, elements that have their equivalents inthe above-described embodiment are denoted by the same referencecharacters as those of their equivalents in the above-describedembodiment.

The partition opening 168 according to this modification includes anelongated hole portion 168 a arranged to extend along the up-downdirection, and an expansion portion 168 b being broad and joined to theelongated hole portion 168 a on the upper side of the elongated holeportion 168 a. A lower end of the elongated hole portion 168 a isarranged in the vicinity of the bottom portion 81 a of the motor chamber81. The elongated hole portion 168 a is arranged to overlap with themotor axis J2 when viewed in the up-down direction. The expansionportion 168 b is arranged to be broader than the elongated hole portion168 a along a horizontal direction. The expansion portion 168 b isrectangular with a longitudinal direction thereof being parallel to thehorizontal direction in plan view. The expansion portion 168 b includesa lower end 168 c arranged to extend along the horizontal direction. Thelower end 168 c is arranged at the aforementioned first liquid level OL.

In the partition opening 168, a region which lies lower than the liquidsurface of the oil O, and a region which lies higher than the liquidsurface, are referred to as a first region S and a second region R,respectively.

FIG. 18 is a graph showing the relationship between the level of theliquid level of the oil O gathered in the lower region of the motorchamber 81 and the area of the first region S according to the presentmodification.

In the case of the present modification, once the liquid level reachesthe first liquid level OL, the oil O flows out through the expansionportion 168 b in addition to the elongated hole portion 168 a, causing arapid increase in the area of the first region S. Accordingly, the flowrate at which the oil O flows from the motor chamber 81 into the gearchamber 82 through the partition opening 168 rapidly increases. Becausethe first liquid level OL is set lower than the lower end of the rotor20, a reduction in the likelihood that the rotation efficiency of therotor 20 will be reduced by the flow resistance of the oil O can beachieved.

Referring to FIG. 1, when the motor 2 is in operation, the second oilpassage 92 feeds the oil O from the oil pool P to the motor 2 through anoperation of the pump 96. In addition, when the motor 2 is in operation,the first oil passage 91 transfers the oil O from the oil pool P to thefirst reservoir 93 through the scraping up of the oil O by thedifferential 5, and feeds the oil O to the inside of the motor 2. Thatis, when the motor 2 is in operation, each of the first oil passage 91and the second oil passage 92 feeds the oil O from the oil pool P to themotor 2. Therefore, when the motor 2 is in operation, the level of theliquid surface of the oil pool P in the lower region of the gear chamber82 is lowered. In addition, since the oil O fed to the motor 2 isgathered in the lower space of the motor chamber 81, the level of theliquid surface of the oil O gathered in the lower region of the motorchamber 81 is raised when the motor 2 is in operation.

Meanwhile, when the motor 2 is in the stopped state, each of the firstoil passage 91 and the second oil passage 92 stops the feeding of theoil O to the motor 2. Thus, a portion of the oil O which has drippeddownwardly of the motor 2 is once gathered in the lower region of themotor chamber 81, and travels into the oil pool P in the lower region ofthe gear chamber 82 through the partition opening 68. Accordingly, whenthe motor 2 is in the stopped state, the level of the liquid surface ofthe oil O gathered in the lower region of the motor chamber 81 islowered, and the level of the liquid surface of the oil pool P in thelower region of the gear chamber 82 is raised.

FIG. 19 is a side view illustrating the arrangement of the gears in thegear chamber 82. Note that, in FIG. 19, the gear housing portion 62 ofthe housing 6 and the bearings arranged to support the shafts are notshown.

Referring to FIG. 19, according to the present embodiment, the level ofthe liquid surface of the oil O gathered in the oil pool P variesbetween the maximum level Lmax and the minimum level Lmin due to the oilO being fed to the oil passage 90 (i.e., the first oil passage 91 andthe second oil passage 92). As illustrated in FIG. 1, the firstreservoir 93 is arranged in the first oil passage 91. In addition, thesecond reservoir 98 and the auxiliary reservoir 95 (not shown in FIG. 1;see FIG. 14) are arranged in the second oil passage 92. Further, the oilO is gathered in the lower region of the motor chamber 81, at which thefirst oil passage 91 and the second oil passage 92 join. Thus, severalplaces at which the oil O is gathered are arranged in the channels ofthe first oil passage 91 and the second oil passage 92. Thus, due to thefeeding of the oil O to the motor 2, the oil O gathered in the oil poolP is transferred to the reservoirs and so on in the aforementionedchannels, so that the level of the liquid surface of the oil pool P islowered. This will result in exposure of the gears in the gear chamber82 from the oil O in the oil pool P, leading to increased rotationefficiency of the gears.

Referring to FIG. 19, a lower end of the second gear 42, which isconnected to the motor 2 and has the greater diameter of a pair of gears(i.e., the second gear 42 and the third gear 43) arranged to rotateabout the intermediate axis J4, is positioned lower than the maximumlevel Lmax of the liquid surface. In addition, the lower end of thesecond gear 42 is positioned higher than the minimum level Lmin of theliquid surface.

Similarly, a lower end of the third gear 43, which is connected to thedifferential 5 and has the smaller diameter of the pair of gears (i.e.,the second gear 42 and the third gear 43) arranged to rotate about theintermediate axis J4, is positioned lower than the maximum level Lmax ofthe liquid surface. In addition, the lower end of the third gear 43 ispositioned higher than the minimum level Lmin of the liquid surface.

The liquid surface of the oil pool P reaches the maximum level Lmax in asituation in which the motor 2 is at rest and the feeding of the oil Ofrom the oil pool P to the motor 2 is interrupted. According to thepresent embodiment, a portion of each of the second gear 42 and thethird gear 43 is arranged to soak in the oil O in the oil pool P whenthe motor 2 is in the stopped state. This arrangement enables the oil Oto immediately spread throughout the tooth faces of the second gear 42and the third gear 43 after the motor 2 is driven, increasing efficiencyin transfer between the gears.

The liquid surface of the oil pool P reaches the minimum level Lmin in asituation in which the motor 2 is operating with a high load and thefeeding of the oil O from the oil pool P to the motor 2 is at itsmaximum. According to the present embodiment, when the motor 2 is inoperation, each of the second gear 42 and the third gear 43 lies higherthan the liquid surface of the oil pool P, preventing a reduction inrotation efficiency of each of the second gear 42 and the third gear 43due to the flow resistance of the oil O. This leads to an increase inoperation efficiency of the motor assembly 1.

A lower end of the ring gear 51, which is included in the differential5, is connected to the reduction gear 4, and is arranged to rotate aboutthe differential axis J5, is positioned lower than the liquid surface nomatter whether the liquid surface is at the maximum level Lmax or at theminimum level Lmin.

According to the present embodiment, at least a portion of the ring gear51 is arranged to lie lower than the liquid surface of the oil O in theoil pool P regardless of the variation in the level of the liquidsurface of the oil pool P. Accordingly, even when the liquid level ofthe oil pool P has been lowered by the operation of the motor 2, thering gear 51 can scrape up the oil O from the oil pool P to feed the oilO to the tooth faces of each gear in the gear chamber 82 to increaseefficiency in transfer of torque between the gears.

With reference to FIG. 1, the flow of the oil O in the oil passage 90which accompanies an operation of the motor assembly 1 will now bedescribed below.

In the case where the motor assembly 1 is installed in the hybridelectric vehicle or the plug-in hybrid vehicle, the vehicle travels inone of an engine mode, in which the vehicle is driven by an enginealone, a motor mode, in which the vehicle is driven by the motor 2alone, and a hybrid mode, in which the vehicle is driven by both theengine and the motor 2.

In the engine mode, the motor 2 is at rest, but the differential 5 isdriven by the engine, and therefore, the oil O is scraped up from theoil pool P. The oil O scraped up is gathered in the first reservoir 93,but is not scattered toward the stator 30 because the rotor 20 is notrotating. Meanwhile, in the engine mode, the pump 96 is not driven, andthe oil O is not fed to the second oil passage 92.

When the vehicle is climbing a hill in the motor mode or the hybridmode, for example, the output of the motor 2 increases, increasing theamount of heat generated by the motor 2. In this case, the dischargerate of the pump 96 is increased to feed more of the oil O to the stator30 to accelerate the cooling. Meanwhile, when the vehicle is travelingdown a hill (i.e., when there is no load on the motor 2), or when themotor 2 has not reached a high-temperature state, such as when thevehicle starts or when the vehicle is used in a cold place, thedischarge rate of the pump 96 is reduced.

The second oil passage 92 is able to adjust the amount of feeding to themotor 2 by the pump 96 in accordance with the temperature of the motor2, the driving mode of the vehicle, and so on. According to the presentembodiment, an increase in efficiency of energy use required to cool themotor 2 can be achieved. This effect can be achieved when the pump 96 isan electrically-driven pump.

Control of the discharge rate of the pump 96 can be performed on thebasis of data of a temperature measured by a temperature sensor providedin the motor 2. In addition, a change in the temperature of the motor 2can be predicted taking into account data of a driving history of thevehicle, a driving condition, the posture of the vehicle, an outside airtemperature, the weight of an occupant(s) and baggage, and so on. Thecontrol may be performed on the basis of the predicted change in thetemperature so that the motor 2 will not come into a high-temperaturestate.

The oil passage 90 according to the present embodiment is able to feedthe oil O to the stator 30 from a plurality of positions, and istherefore able to efficiently cool the whole stator 30. In addition,according to the present embodiment, the oil O functions as both acooling oil and a lubricating oil. This eliminates the need to provide achannel for the cooling oil and a channel for the lubricating oilseparately, leading to a cost reduction.

The oil O, which is used to cool the motor assembly 1, is used tolubricate the differential 5 and the reduction gear 4. Therefore,contaminants, such as, for example, metal particles generated bymechanical contact, may intrude into the oil O. The contaminants maylower fluidity of the oil O in the first oil passage 91 and the secondoil passage 92. The contaminants are removed by regular replacement ofthe oil O. A means for capturing the contaminants may be arranged in oneor each of the first oil passage 91 and the second oil passage 92. Forexample, as illustrated in FIG. 12, permanent magnets 98 m may be placedat the second reservoir 98 to magnetically capture the contaminants toprevent a spread of the contaminants. In this case, the lowering of thefluidity of the oil O can be reduced or prevented.

The motor axis J2, the intermediate axis J4, and the differential axisJ5 are arranged to extend in parallel with one another along ahorizontal direction. Each of the intermediate axis J4 and thedifferential axis J5 is arranged lower than the motor axis J2.Accordingly, each of the reduction gear 4 and the differential 5 isarranged lower than the motor 2.

A line segment that imaginarily joins the motor axis J2 and theintermediate axis J4 when viewed in the axial direction of the motoraxis J2 is defined as a first line segment L1, a line segment thatimaginarily joins the intermediate axis J4 and the differential axis J5when viewed in the axial direction of the motor axis J2 is defined as asecond line segment L2, and a line segment that imaginarily joins themotor axis J2 and the differential axis J5 when viewed in the axialdirection of the motor axis J2 is defined as a third line segment L3.

According to the present embodiment, the second line segment L2 extendssubstantially along a horizontal direction. That is, the intermediateaxis J4 and the differential axis J5 are arranged side by sidesubstantially in the horizontal direction. This allows the reductiongear 4 and the differential 5 to be arranged side by side along thehorizontal direction, which leads to a reduced vertical dimension of themotor assembly 1. In addition, the oil O scraped up by the differential5 can be efficiently fed onto the reduction gear 4. Thus, the oil O canbe fed onto the tooth faces of the gears of the reduction gear 4 toincrease the efficiency in transfer between the gears. Note that each ofthe diameters of the gears (i.e., the second gear 42 and the third gear43) arranged to rotate about the intermediate axis J4 is smaller thanthe diameter of the ring gear 51, which is arranged to rotate about thedifferential axis J5. According to the present embodiment, since thesecond line segment L2 extends substantially along the horizontaldirection, the intermediate axis J4 and the differential axis J5 arearranged substantially along the horizontal direction. Accordingly,depending on the level of the liquid surface of the oil pool P, only thering gear 51 may soak in the oil pool P, with neither of the second gear42 and the third gear 43 soaking in the oil pool P. Thus, a reduction inthe rotation efficiency of each of the second gear 42 and the third gear43 can be prevented while allowing the ring gear 51 to scrape up the oilO in the oil pool P.

Note that, when the second line segment L2 is described as extendingsubstantially along a horizontal direction in the description of thepresent embodiment, it means that the second line segment L2 extends atan angle of −10° to +10° both inclusive to the horizontal direction.

According to the present embodiment, an angle θ defined between thesecond line segment L2 and the third line segment L3 is in the range of30°±5°. This arrangement makes it possible to realize a desired gearratio while allowing the oil O scraped up by the differential 5 toincrease the efficiency in transfer between the first gear 41 and thesecond gear 42.

If the angle θ exceeded 35°, it would be difficult to feed the oilscraped up by the differential onto the gear (i.e., the first gear)arranged to rotate about the motor axis. This might lead to a reductionin the efficiency in transfer between the first gear and the secondgear. On the other hand, if the angle θ were smaller than 25°, it wouldbe difficult to realize a desired gear ratio between the three axes(i.e., the motor axis, the intermediate axis, and the differential axis)due to an inability to arrange the gear on an output side in a course oftransfer to have a sufficient size.

According to the present embodiment, the first line segment L1 extendssubstantially along the vertical direction. That is, the motor axis J2and the intermediate axis J4 are arranged one above the othersubstantially along the vertical direction. This allows the motor 2 andthe reduction gear 4 to be arranged one above the other along thevertical direction, which leads to a reduced horizontal dimension of themotor assembly 1.

In addition, arranging the first line segment L1 to extend substantiallyalong the vertical direction contributes to arranging the motor axis J2closer to the differential axis J5 so that the oil O scraped up by thedifferential 5 can be fed onto the first gear 41, which is arranged torotate about the motor axis J2. This leads to an increase in theefficiency in transfer between the first gear 41 and the second gear 42.

Note that, when the first line segment L1 is described as extendingsubstantially along the vertical direction in the description of thepresent embodiment, it means that the first line segment L1 extends atan angle of −10° to +10° both inclusive to the vertical direction.

The length L1 of the first line segment, the length L2 of the secondline segment, and the length L3 of the third line segment satisfy thefollowing relationship:L1:L2:L3=1:1.4 to 1.7:1.8 to 2.0.

In addition, the reduction ratio of a speed reduction mechanism betweenthe motor 2 and the differential 5 is arranged to be in the range of 8to 11 both inclusive.

According to the present embodiment, the desired gear ratio (in therange of 8 to 11 both inclusive) can be realized while maintaining theabove-described positional relationship between the motor axis J2, theintermediate axis J4, and the differential axis J5.

FIG. 20 is a diagram illustrating the parking mechanism 7, which can beadopted in the motor assembly 1 according to the present embodiment.

The parking mechanism 7 is effective in the case where the motorassembly 1 is used in an electric vehicle (EV).

A manual transmission vehicle driven by an engine can be braked not onlyby applying a hand brake but also by setting a transmission in aposition other than a neutral position to apply a load to the engine. Anautomatic transmission vehicle can be braked not only by applying a handbrake but also by setting a shift lever in a parking position to lockthe transmission.

Meanwhile, the electric vehicle has no brake mechanism to brake thevehicle other than a hand brake, and is therefore required to have theparking mechanism 7 in the motor assembly 1.

The parking mechanism 7 includes a ring-shaped parking gear 71, aparking pawl 72, a parking rod 73, and a parking lever 74. The parkinggear 71 is arranged to be coaxial with each of the second gear (i.e.,the intermediate gear) 42, the third gear 43, and the intermediate shaft45. The parking gear 71 is fixed to the intermediate shaft 45. Theparking pawl 72 includes a projection portion 72 a arranged to be fittedinto a groove of the parking gear 71 to stop rotation of the parkinggear 71. The parking rod 73 is connected to the parking pawl 72 to movethe projection portion 72 a along a radial direction of the parkinggear. The parking lever 74 is connected to the parking rod 73 to drivethe parking rod 73.

When the motor 2 is in operation, the parking pawl 72 is separated fromthe parking gear 71. Meanwhile, when the shift lever is in the parkingposition, the parking pawl 72 is engaged with the parking gear 71 tostop the rotation of the parking gear 71.

A parking motor (not shown) connected to the parking lever is used tocontrol the parking pawl 72. Use of the parking motor enables theparking mechanism 7 to be driven by electricity, allowing components todrive the parking mechanism 7 to be simple. In addition, the use of theparking motor allows the parking pawl 72 to be driven with a pushbutton, a paddle lever, or the like, providing improved operability to adriver. This mechanism is called a shift-by-wire system.

Note that the parking mechanism 7, which is an electrically-drivenmechanism using the shift-by-wire system, may be replaced with a manualparking mechanism. That is, the parking pawl may be driven by a drivermechanically pulling a wire connected to the parking lever.

According to the present embodiment, the parking mechanism 7 is arrangedaround the intermediate shaft 45. A reduction in a braking torque tostop the rotation of the parking gear 71 can thus be achieved comparedto the case where the parking mechanism 7 is arranged around a gear in astage subsequent to the intermediate shaft along a course of torquetransfer from the motor 2 to the axles 55. Thus, a reduced size and areduced weight of the parking mechanism can be achieved. In addition, inthe case where the parking mechanism 7 is an electrically-drivenmechanism, a small-sized motor can be adopted as the parking motor.Further, in the case where a manual parking mechanism is used as theparking mechanism, an operational load on the driver can be reduced.

In addition, according to the present embodiment, the parking mechanism7 is arranged on the lower side of the reduction gear 4. Accordingly,the parking pawl 72 soaks in the oil O of the oil pool P, and thisenables the oil O to intervene between the parking gear 71 and theprojection portion 72 a of the parking pawl 72 to facilitate engagementand disengagement of the projection portion 72 a.

Note that the parking mechanism 7 according to the present embodiment ismerely an example, and that another structure known in the art mayalternatively be adopted. Also note that the parking mechanism 7 mayalternatively be arranged to apply a braking force to the ring gear 51or to the shaft 21 connected to the motor 2.

FIG. 21 is a partial sectional view illustrating a separating mechanism107 of a motor assembly 101 according to Modification 1.

The motor assembly 101 according to a modification, Modification 1,which has the separating mechanism 107 arranged along a course of torquetransfer from a motor 2 to axles 55, will now be described below. Themotor assembly 101 according to the present modification is differentmainly in that the separating mechanism 107 is arranged in a shaft 121of the motor 2. Note that, in the following description, elements thathave their equivalents in the above-described embodiment are denoted bythe same reference characters as those of their equivalents in theabove-described embodiment.

The separating mechanism 107 is provided in the case where the motorassembly 101 is installed in a hybrid electric vehicle (HEV) or aplug-in hybrid vehicle (PHV). Each of the hybrid electric vehicle andthe plug-in hybrid vehicle travels in one of an engine mode, in whichthe vehicle is driven by an engine alone, a motor mode, in which thevehicle is driven by the motor 2 alone, and a hybrid mode, in which thevehicle is driven by both the engine and the motor 2. The separatingmechanism 107 is arranged to separate a power transmission mechanism(i.e., a rotor 20 of the motor 2, a reduction gear 4, and a differential5) of the motor assembly 101 from the axles 55 to prevent the motor 2 atrest from becoming a load when the vehicle is traveling in the enginemode.

Referring to FIG. 21, in the present modification, the shaft 121includes a first shaft portion 121A, a connecting shaft portion 121C,and a second shaft portion 121B, which are arranged coaxially with oneanother, and the separating mechanism 107, which is arranged between theconnecting shaft portion 121C and the second shaft portion 121B. Thefirst shaft portion 121A, the connecting shaft portion 121C, and thesecond shaft portion 121B are arranged in the order named along theaxial direction. That is, the connecting shaft portion 121C is arrangedbetween the first shaft portion 121A and the second shaft portion 121B.

The shaft 121 is a hollow shaft in which hollow portions 122, each ofwhich has an inner circumferential surface extending along a motor axisJ2, are defined. The hollow portions 122 include a first hollow portion122A arranged inside the first shaft portion 121A, a second hollowportion 122B arranged inside the second shaft portion 121B, and a thirdhollow portion 122C arranged inside the connecting shaft portion 121C.The first hollow portion 122A, the second hollow portion 122B, and thethird hollow portion 122C are arranged along the axial direction, andare in communication with one another.

The first shaft portion 121A is arranged in a motor chamber 81 of ahousing space 80. The first shaft portion 121A is arranged radiallyinside of a stator 30, and is arranged to pass through a rotor core 24along the motor axis J2.

The first shaft portion 121A includes a first end portion 121 e arrangedon an output side (i.e., a side closer to the reduction gear 4).

The first end portion 121 e is arranged to pass through an insert hole61 f defined in a partition 61 c from a side on which the motor chamber81 lies. The first hollow portion (i.e., a second recessed portion) 122Ais arranged to open in a surface of the first end portion 121 e whichfaces in the axial direction. The first end portion 121 e is rotatablysupported by a first bearing 89, which is arranged to be in contactwith, and to be held by, a surface of the partition 61 c which facesonto the motor chamber 81.

Alignment of the first shaft portion 121A can be accomplished at aposition on the side on which the motor chamber 81 lies in a housing 6with the first bearing 89 being arranged to be in contact with, and tobe held by, the surface of the partition 61 c which faces onto the motorchamber 81. Thus, alignment of the first shaft portion 121A with respectto the stator 30 can be achieved with high accuracy.

The connecting shaft portion 121C is arranged in the insert hole 61 f.The connecting shaft portion 121C is rotatably supported by a secondbearing 188A, which is arranged to be in contact with, and to be heldby, a surface of the partition 61 c which faces onto a gear chamber 82.The second bearing 188A is a ball bearing. The connecting shaft portion121C includes a shoulder surface 121 q arranged to face toward thepartition 61 c. The shoulder surface 121 q is arranged to be in contactwith an inner race of the second bearing 188A.

According to the present modification, the second bearing 188A is heldby the surface of the partition 61 c which faces onto the gear chamber82. This arrangement makes it possible to fit the connecting shaftportion 121C to the first shaft portion 121A after the alignment of thefirst shaft portion 121A is finished. Thus, a process of fitting theconnecting shaft portion 121C can be simplified.

The second bearing 188A is arranged to have an outside diameter greaterthan an outside diameter of the first bearing 89. When the separatingmechanism 107 is operated, heavy axial and circumferential loads areapplied to the second bearing 188A. Having a diameter greater than thatof the first bearing 89, the second bearing 188A according to thepresent modification is able to ensure sufficient strength thereofagainst the loads applied when the separating mechanism 107 is operated.

The connecting shaft portion 121C includes a second end portion 121 f, athird end portion 121 g, and a connection flange portion 121 h.

The second end portion 121 f is arranged to project into the motorchamber 81. The second end portion 121 f is arranged on a side closer tothe first shaft portion 121A, and is coupled to the first end portion121 e of the first shaft portion 121A. The second end portion 121 f ishoused in the first hollow portion 122A, which is arranged to open inthe first end portion 121 e. An outer circumferential surface of thesecond end portion 121 f is fitted to an inner circumferential surfaceof the first hollow portion 122A. The fitting of the second end portion121 f in the first hollow portion 122A contributes to a reduced radialdimension of a joint between the first end portion 121 e and the secondend portion 121 f. This in turn contributes to securing a space in whichto arrange the first bearing 89 radially outside of the first endportion 121 e.

The third end portion 121 g is arranged to project into the gear chamber82. The third end portion 121 g is arranged on a side opposite to thesecond end portion 121 f and closer to the second shaft portion 121B. Afirst recessed portion 121 p is defined at an end portion of the thirdend portion 121 g which faces in the axial direction.

The connection flange portion 121 h is arranged to extend radiallyoutward at the third end portion 121 g. The connection flange portion121 h is arranged to have a diameter greater than a minimum diameter ofthe insert hole 61 f.

According to the present modification, the connecting shaft portion 121Cand the first shaft portion 121A are defined by separate members.Accordingly, it is possible to fit the connecting shaft portion 121C tothe first shaft portion 121A after a process of assembling the motor 2,and thus, the assembly can be performed in the same order as when theseparating mechanism 107 is not provided. Accordingly, the shapes ofparts other than the shaft 121 can be the same as when the separatingmechanism 107 is not provided. That is, according to the presentmodification, commonality of parts can be achieved between the motorassembly 101, which includes the separating mechanism 107, and the motorassembly 1, which does not include the separating mechanism 107. Inaddition, since the assembly can be performed in the same orderregardless of whether the separating mechanism 107 is provided, it ispossible to prevent the shapes of the parts from becoming complicated,and to prevent an increase in the number of parts. Thus, the motorassembly 101 according to the present modification is able to achievehigh versatility and a low cost.

The second shaft portion 121B is arranged in the gear chamber 82 of thehousing space 80.

The second shaft portion 121B includes a fourth end portion 121 i and afifth end portion 121 j.

The fourth end portion 121 i is arranged on a side closer to the thirdend portion 121 g of the connecting shaft portion 121C. The fourth endportion 121 i and the connection flange portion 121 h of the connectingshaft portion 121C can be selectively separated from each other by theseparating mechanism 107 to cut off transfer of power therebetween.

The fourth end portion 121 i is housed in the first recessed portion 121p defined at the third end portion 121 g. A needle bearing (i.e., abearing) 121 n is arranged in a radial gap between the third end portion121 g and the fourth end portion 121 i. That is, according to thepresent modification, the second shaft portion 121B is rotatablysupported by the connecting shaft portion 121C at the fourth end portion121 i. Thus, according to the present modification, in the case wherethe second shaft portion 121B and the connecting shaft portion 121C havebeen separated from each other by the separating mechanism 107, stableholding thereof can be achieved without hindering relative rotationtherebetween. Note that this effect can be achieved when one of thethird end portion 121 g and the fourth end portion 121 i includes thefirst recessed portion, in which another one of the third end portion121 g and the fourth end portion 121 i is housed with the needle bearing121 n interposed therebetween.

Note that, although the needle bearing 121 n according to the presentmodification is arranged to include a plurality of columnar membersarranged in an annular shape, another bearing mechanism, such as, forexample, a ball bearing, may be used in place of the needle bearing 121n. However, adoption of the needle bearing leads to reduced radialdimensions of the third end portion 121 g and the fourth end portion 121i, and a reduced size of the motor assembly 101.

As mentioned above, the hollow portions 122, which extend in the axialdirection and are in communication with one another, are defined in thefirst shaft portion 121A, the connecting shaft portion 121C, and thesecond shaft portion 121B. As in the above-described embodiment, an oilO to cool an inside of the motor 2 is fed into the hollow portions 122from a side on which the second shaft portion 121B lies toward a side onwhich the first shaft portion 121A lies.

According to the present modification, the connecting shaft portion 121Cand the second shaft portion 121B are connected to each other throughthe needle bearing 121 n. Thus, the third hollow portion 122C of theconnecting shaft portion 121C and the second hollow portion 122B of thesecond shaft portion 121B can be connected to each other. Thus, thehollow portions 122 can be used as an oil flow passage, being able toreceive the feeding of the oil O.

The fifth end portion 121 j is arranged on a side opposite to the fourthend portion 121 i. The fifth end portion 121 j is rotatably supported bya third bearing 188B, which is held by the housing 6. That is, thesecond shaft portion 121B is supported by the third bearing 188B at thefifth end portion 121 j.

According to the present modification, the second shaft portion 121B issupported by the two bearings (i.e., the needle bearing 121 n and thethird bearing 188B) arranged in the axial direction. Similarly, theconnecting shaft portion 121C is supported by the two bearings (i.e.,the second bearing 188A and the needle bearing 121 n) arranged in theaxial direction. Being rotatably supported at two positions along theaxial direction, each of the second shaft portion 121B and theconnecting shaft portion 121C is able to stably rotate without wobbling.

A first gear 41 is arranged on an outer circumferential surface of thesecond shaft portion 121B. The first gear 41 is arranged between thefourth end portion 121 i and the fifth end portion 121 j. The first gear41 is arranged to transfer power to a second gear 42 of the reductiongear 4. According to the present modification, the first gear 41 isarranged between the second bearing 188A and the third bearing 188B.Accordingly, the first gear 41 is able to rotate stably with respect tothe motor axis J2, and is able to stably transfer a torque generated bythe motor 2 to the second gear 42.

The separating mechanism 107 is arranged to surround the connectionflange portion 121 h of the connecting shaft portion 121C and the fourthend portion 121 i of the second shaft portion 121B from radiallyoutside. The separating mechanism 107 is arranged to make a switchbetween a condition in which the connection flange portion 121 h and thefourth end portion 121 i are not mechanically coupled to each other, anda condition in which the connection flange portion 121 h and the fourthend portion 121 i are coupled to each other, using a driving portion175.

The separating mechanism 107 is arranged between an axial end surface ofthe motor 2 and the first gear 41 in the axial direction. The motorassembly 101 is arranged to have a triaxial structure, having the motoraxis J2, an intermediate axis J4, and a differential axis J5. Inaddition, a third gear 43 is arranged between the axial end surface ofthe motor 2 and the first gear 41 in the axial direction. The third gear43 is arranged to rotate in synchronism with the second gear 42, whichis connected to the first gear 41. A gap larger than the thickness ofthe third gear 43 is arranged between the axial end surface of the motor2 and the first gear 41. According to the present modification, theseparating mechanism 107 is arranged between the axial end surface ofthe motor 2 and the first gear 41. That is, the third gear 43 and theseparating mechanism 107 are arranged at positions axially overlappingwith each other. Thus, an effective use of an interior space of the gearchamber 82 can be made to achieve a reduced size of the motor assembly101.

According to the present modification, the separating mechanism isarranged in the shaft 121 of the motor 2. That is, the separatingmechanism 107 is arranged at a position at which the torque is lowestalong a course of transfer of power from the motor 2 to the axles 55.According to the present modification, the torque transferred throughthe separating mechanism 107 is low, and therefore, the separatingmechanism 107 may have a relatively small size.

The separating mechanism 107 according to the present modification iscalled a rotation synchronizing device or a synchromesh mechanism. Notethat the separating mechanism 107 according to the present modificationis merely an example. For example, a dog clutch mechanism or a multipleclutch mechanism may be adopted as the separating mechanism.

The separating mechanism 107 includes a sleeve 171, a clutch hub 172, asynchronizer ring 173, a key 174, and the driving portion (not shown).

The clutch hub 172 is fixed to the outer circumferential surface of thesecond shaft portion 121B. The clutch hub 172 is arranged to rotateabout the motor axis J2 together with the second shaft portion 121B.External splines are defined in an outer circumference of the clutch hub172.

The sleeve 171 is arranged to be capable of moving along the axialdirection. The sleeve 171 is arranged to mesh with the external splinesof the clutch hub 172 to rotate integrally with the clutch hub 172. Inaddition, splines are defined in an inner circumferential surface of thesleeve 171. The splines of the sleeve 171 are fitted into splinesdefined in an outer circumferential surface of the connection flangeportion 121 h after the clutch hub 172 and the connection flange portion121 h rotate in synchronism with each other. The second shaft portion121B and the connecting shaft portion 121C are thus coupled to eachother.

The key 174 is held by the sleeve 171. The key 174 is capable of movingin the axial direction together with the sleeve 171. The key 174 isarranged to cause the splines defined in the sleeve 171 and the splinesdefined in the connection flange portion 121 h to be in phase.

The synchronizer ring 173 is arranged to be capable of moving in theaxial direction together with the sleeve 171. The synchronizer ring 173includes a tapered surface arranged to increase in inside diametertoward a side on which the connection flange portion 121 h lies.Meanwhile, the connection flange portion 121 h includes a boss portionarranged to project to a side on which the synchronizer ring 173 liesalong the axial direction. The boss portion includes a tapered surfacearranged opposite to the synchronizer ring 173. The synchronizer ring173 and the connection flange portion 121 h are arranged to rotate insynchronism through a contact between the respective tapered surfacesthereof.

The driving portion, which is not shown, is connected to the sleeve 171.The driving portion is arranged to cause the sleeve 171 to move in theaxial direction.

FIG. 22 is a schematic diagram illustrating a situation in which themotor 2 and the reduction gear 4 are connected to each other through theseparating mechanism 107, and FIG. 23 is a schematic diagramillustrating a situation in which the motor 2 and the reduction gear 4have been separated from each other by the separating mechanism 107.

As mentioned above, the motor assembly 101, which includes theseparating mechanism 107, is installed in the hybrid electric vehicle orthe plug-in hybrid vehicle. When a switch has been made in such avehicle between a mode in which the vehicle travels using only power ofthe engine and a mode in which the vehicle travels using power of themotor 2, the driving portion 175 operates to make a switch betweenconnection and separation of the connecting shaft portion 121C and thesecond shaft portion 121B.

Control related to the separating mechanism 107 will now be describedbelow. When the separating mechanism 107 makes a switch from a separatedcondition to a connected condition, the rotation rate of the secondshaft portion 121B is first calculated from the rotation rates of theaxles 55. Next, the rotation rate of the motor 2 is increased to thecalculated rotation rate of the second shaft portion 121B. While therotation rate of the motor 2 is increased, the sleeve is caused to moveby the driving portion 175, and connection between the second shaftportion 121B and the connecting shaft portion 121C is established.Thereafter, a position at which the connection between the second shaftportion 121B and the connecting shaft portion 121C is completed iscalculated from the total number of rotations of the driving portion175. Finally, an equality between the rotation rate of the motor 2 andthe rotation rate of the second shaft portion 121B calculated from therotation rates of the axles 55 is detected to finally determine that ajoined condition is complete.

Various components of the motor assembly 1, including the motor 2, thepump 96, the driving portion 175 of the separating mechanism 107, andthe parking motor of the parking mechanism 7, are controlled in acentralized manner by a microcontroller unit (MCU). The microcontrollerunit may be arranged either integrally with the motor assembly 1 orexternal to the motor assembly 1.

The motor assembly 1 is applicable to any of the hybrid electric vehicle(HEV), the plug-in hybrid vehicle (PHV), and the electric vehicle (EV).In addition, the motor assembly 1 is applicable not only to a passengervehicle but also to a load-carrying vehicle (i.e., a truck), etc. Themotor assembly 1 may be installed on either a front side or a rear sideof the vehicle, but is preferably installed on the rear side. The motorassembly 1 according to the present embodiment has a relatively smallvertical dimension, and can therefore be compactly installed even on therear side, where only a limited installation space is available becauseof constraints of a trunk and a ground clearance.

Features of the above-described preferred embodiments and themodifications thereof may be combined appropriately as long as noconflict arises.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

The invention claimed is:
 1. A motor assembly comprising: a motor with acentral axis extending in an axial direction; a housing including ahousing space to house the motor; oil in a vertically lower region ofthe housing space; and an oil passage to lead the oil from thevertically lower region of the housing space through the motor to thevertically lower region of the housing space; wherein the housing spaceof the housing is divided into a motor chamber and a gear chamber by apartition; an oil pool is provided at a bottom portion of the gearchamber; a bottom portion of the motor chamber is vertically higher thanthe bottom portion of the gear chamber; the partition includes apartition opening; the oil passage includes an electric pump, a cooler,a first flow passage, a second flow passage, and a third flow passage;the first flow passage connects the oil pool and the electric pump toeach other; the second flow passage connects the electric pump and thecooler to each other; the third flow passage connects the cooler and themotor chamber to each other; and the oil gathered at the bottom portionof the motor chamber travels into the oil pool through the partitionopening.
 2. The motor assembly according to claim 1, wherein a lower endof the partition opening is vertically lower than a lower end of thestator.
 3. The motor assembly according to claim 1, wherein a recessedportion is recessed radially outward and defined in an inner peripheralsurface of a peripheral wall portion of the housing; the recessedportion extends along the axial direction; and the partition opening isat the recessed portion defined in the inner peripheral surface of theperipheral wall portion.